There's a good article in the Telegraph today showing you ways of avoiding the single supplement when booking a Holiday.  It lists 6 tips you can try:

1. Negotiate
Holidaymakers have the upper hand over tour operators and hotels at the moment. If you are booking at a time when the hotel is unlikely to be sold out or is offering special deals, phone and ask the tour operator whether it will waive the supplement.

2. Cut out the middle man
If you are prepared to book independently, try contacting the hotel by phone or email to negotiate the best possible rate for a single room or single occupancy.

3. Travel in the shoulder season
In the Mediterranean that means May and June and September and October. Many hotels are quieter at these times and more willing to offer better rates for single occupancy. Some tour operators and cruise companies highlight dates in these months when they are offering tours and hotel stays which are reserved for single travellers or which don't attract supplements.

4. Book with an operator that specialises in singles holidays
Below are six companies that offer various types of holiday specificially aimed at single travellers. Some offer tours with a balanced number of men and women; some are relaxed about such things. Mostly, they do not charge supplements, but offer a single or double room for sole occupancy – though that does not mean they are necessarily cheaper overall than an operator which prices in a different way, so compare prices before booking).

Friendship Travel (0871 200 2035; friendshiptravel.com); Just You (0800 112 3311; justyou.co.uk); Small Families (0845 900 0895; smallfamilies.co.uk) which is aimed at single-parent families; Solitair Holidays (0845 123 5515; singlesholidays.com); Travel One (0844 576 6866; travelone.co.uk); Solos Holidays (0844 815 0001; solosholidays.co.uk).

5. Consider sharing
Many tour operators will offer to try to arrange a shared room with another single traveller of the same sex. Alternatively, you could try to find a travelling companion through a specialist singles website. Two membership sites which put a particular emphasis on travel are singleagain.co.uk and companions2travel.co.uk (both charge £25 a year for membership, but have cheaper, trial periods).

6. Consider adventure travel
Trips where most nights are spent camping or in refuges, youth hostels or simple lodges, and food is paid per person out of a kitty, are far less likely to charge significantly more for single bookings.

Source: The Telegraph