I have been to Phuket which was an amazing holiday and pretty cheap. We booked through Best@Asia and they were great.
Most of the beaches and islands around Thailand are very good value and great, relaxing holidays - great snorkelling, great food and loads of trips to go on

Phuket is good because it's a small island but has several decent towns to visit and is easy and cheap to get around. Phuket Town has lots of shops and a great night market, Patong is much more touristy but has great bars and the night life is somehting to see.
If you stay along the coast, away from the towns then it's only a 30 minute Tuk-tuk ride to most places. We stayed in Cape Panwa region
Wherever you go in Asia though you'll have a great time - amazing place