1. The rapture is plainly taught in Scripture.  Believers will be physically removed from the earth according to 1 Thessalonians 4:16-17.  As soon as I hear someone say, "the rapture is not in the Bible," I know they've already lost the argument.  If you think 1 Thessalonians 4:17 is just allegory then there is nothing further to discuss.  If we can't agree on the basic meaning of words then we are not going to agree on anything.  The passage says Believers will be "caught up" from the earth and will meet the Lord in the sky.  Some even go so far as to argue that the word "rapture" is not in the Bible.  I'm utterly dumbfounded by that argument, which is the logical equivalent of saying there is no God because the word Yahweh is not in the Bible.  The word Yahweh is in the Bible - in the original Hebrew, just as the word rapture (specifically rapturo) is in the Latin Bible.  In the original Greek passage of 1 Thessalonians 4, the rapture is called the harpazo.  It's the exact same thing and silly word games and semantic-twisting will never change that fact.

2. Constant expectancy (a.k.a. imminency).  The early Church was well aware of the many events that had to transpire during the final years before Jesus returned to Israel.  The Apostles were intimately aware of these details because Jesus had shared the knowledge with them in His Olivet Discourse.  They knew that an antichrist (called the "man of lawlessness") would arise, the Temple would be rebuilt, and several years of great tribulation would ensue.  Yet the consistent sense of New Testament Scripture is that early Believers lived with a constant sense of expectancy for the Lord's imminent appearing.  Mid-trib, pre-wrath, and post-trib proponents handle these "imminency" Scriptures in a variety of creative ways, but I have never been presented with a satisfactory argument.  Only the pre-trib doctrine interprets the many Scriptures that describe an imminent appearing of Christ with their prima facie meaning.  More about this here.

3. Believers are going to Heaven.  Jesus told His disciples in John 14:2-3 that He was leaving them, but would come back and take them to be with Him in His Father's house (see also Hebrews 12:22-24).  This promise is as clear as day.  We know where Jesus went - He went to His Father's house in Heaven and sat down at His right hand.  The prophecy in Hosea 5:15 makes this even more clear.  While this promise doesn't necessarily rule out mid-trib or pre-wrath views, it does rule out many if not most post-trib theories.

4. The pre-trib rapture is built on promises.  Pre-tribbers are often mocked as being proponents of "easy-escapism", but the mockery doesn't change what the Bible plainly says in 1 Thessalonians 1:10, 1 Thessalonians 5:9, Luke 21:36, and Revelation 3:10.  Believers escape before the Time of Jacob's Trouble.

5. The Church is conspicuously absent from Revelation chapters 5 through 19.  The Book of Revelation is primarily about the events transpiring during the Tribulation and the Church is not mentioned one time between chapters 5 and 19.  Even more, Revelation 4:1 is a type or shadow of the rapture where the Apostle John is "caught up" to Heaven at the sound of a trumpet.  The 24 elders, which most biblical scholars consider to be a picture of the glorified Church in Heaven, are already present in Heaven in chapter 4 and from Heaven John and the elders are able to witness the Tribulation events occurring "below" on earth.  The only allusion to the Church in these chapters is found in Revelation 12, specifically Revelation 12:5, where a male child that represents the corporate Church is raptured to Heaven before Israel (the woman) enters into Tribulation.

6. Consistency in symbolism.  Noah and his family escape before the Flood comes.  As a matter of fact, God commanded Noah and his family to enter the ark seven days before the Flood came (Genesis 7:1-10) just as the Church will escape seven years before God's wrath is fully poured out.  Similarly, Lot and his family escaped from Sodom before the city was destroyed.  Furthermore, it wasn't just happenstance that Noah and Lot escaped before judgment - in Genesis 18:22-33 we learn that the reason they escaped beforehand was because God's very character was at stake.

Also, Joseph was a "type" of the Church and he was removed from his land and ended up in Egypt where he became royalty just as the Church will be raptured from this lowly earth and enthroned in Heaven (Revelation 3:21, 4:4).  Then the land of Israel underwent seven years of terrible famine while Joseph was tucked safely away in palaces of splendor.  A foreshadowing of the Time of Jacob's Trouble if there ever was one since Jacob himself, and his other sons, were suffering in the famine.

Another example was the Prophet Daniel who had been elevated to a high position in Babylon when Shadrach, Meshach, and Abednego were thrown into the fiery furnace.  Shadrach, Meshach, and Abednego were a shadow of Israel being protected during the Tribulation while Daniel was a shadow of the Church, which will be far away from harm.  Though later, Daniel himself becomes a shadow of Israel when he is protected in the midst of the den of lions.

7. The "departure" of the Church.  2 Thessalonians 2:3 contains the smoking gun: the Greek word apostasia here simply means "departure" rather than "falling away".  The first English Bibles all translated this word as "departure" as did some of the earliest Bibles such as the Latin Vulgate.  The context in the passage (gathering of the Church, removal of the restrainer, and revealing of the antichrist) in addition to the use of a definite article in verse 3, make this Scripture almost certainly a description of the rapture of the Church.  While translating apostasia as "departure" in 2 Thessalonians 2:3 is not necessary to believe in a pre-trib rapture and some pre-tribbers think the rapture is not mentioned in verse 3, if apostasia does refer to the rapture in this verse then on the basis of this passage alone, mid-trib, pre-wrath, and post-trib theories would be completely disproven.  J.D. Farag recently expressed some doubt about this, but I think he needs to study this out on his own.  I've read the various rebuttals to the 2 Thessalonians 2:3 rapture argument, such as those presented by Robert Gundry, and none of them seem particularly convincing.  You can read more about this here, here, and here.

2 Thessalonians 2 has another strong bit of evidence for the pre-trib rapture, which can be found in verses 6-7.  We learn quite clearly that the man of lawlessness (the antichrist) cannot be revealed until a certain restrainer is removed.  Most commentaries regard the restrainer to be the Holy Spirit working in and through the Church.  The removal of the restrainer necessitates a pre-tribulational rapture.

8. It upholds a proper dispensational understanding of Scripture.  Jesus was sent "only to the lost sheep of Israel", yet when His own people rejected Him, God turned His attention to the Gentiles - primarily through Paul, Barnabas, and company, but also through the Apostles themselves.  Daniel's 70 weeks of years, a period set by God to redeem Israel, paused at the end of the 69th week when Jesus was crucified.  This pause is commonly called the Church Age or the Age of Grace and it won't end until the 70th week begins (see Acts 15:12-16).  This 70th week serves two primary purposes: first, the national salvation of Israel (Romans 11:26), and second, a cataclysmic global judgment on the Gentile nations.  The Church is not in view anywhere in Daniel's 70th week.  Even more - the Tribulation is called the "Time of Jacob's Trouble" (Jeremiah 30:7).

9. The pre-trib rapture was not invented in the 19th century.  Nearly as silly as arguing that the rapture is not in the Bible, is arguing that the pre-trib rapture was invented in the 19th century.  Detractors have often attributed the pre-trib rapture's origins to a supposed vision from one Margaret MacDonald in 1830, yet MacDonald never described a pre-trib rapture.

Additionally, it is well known among Bible scholars that whether wrong or right, pre-trib beliefs go back at least to the 18th century, and likely to the early Church.  You can read more about this here, here, and here.

10. The woman in labor seals the deal.  The discovery of a literal astronomical alignment that fits with what is described in Revelation 12 has personally ended the debate for me.  Once we discovered that Revelation 12 should be taken for what it plainly says rather than allegorized and that it describes an actual, future event, the passage suddenly unlocked the meaning of a whole host of Scriptures in both the Old and New Testaments that refer to a "woman in labor" as the primary symbol of the beginning of the Tribulation (see Isaiah 13:6-13, Isaiah 26:17-21, Isaiah 66:7-11, Jeremiah 30:4-11, Jeremiah 49:23-27, Micah 5:3, Matthew 24:8, Mark 13:8, and 1 Thessalonians 5:3).  The woman represents Israel and the child in Revelation 12:5 appears to be a symbol of the Church and this particular child is said to be "raptured" to Heaven.  The timing of this child's birth and rapture?  Before the woman goes into labor (Isaiah 66:7-8).