I agree with PETEFLYS that you are being too aggressive with only 8-9 days. 2-3 days in Bangkok are a must in my opinion. If you are specifically looking for beach, diving and partying I'd say head to Phuket next. Plenty to do and you can grab a tour that will take you out to some beautiful islands. I'm not that into beaches so I'd prefer to head up to Chiang Mai or Chiang Rai rather than down to Phuket. If you are looking for a party scene but not all that interested in diving or boat trips then Pattaya would be more convenient within such a short trip than say Koh Phangan. That said, I've never been to Koh Phangan, Koh Samui and some of the other islands. I just figure you'll want to limit the amount of travel time between different areas.

This section is filled with threads that will help you with what to do in these various places.

http://www.flyertalk.com/forum/thail...rief-plan.html

http://www.flyertalk.com/forum/thail...ok-eating.html

http://www.flyertalk.com/forum/thail...-thailand.html

http://www.flyertalk.com/forum/thail...ning-help.html

http://www.flyertalk.com/forum/thail...itinerary.html

http://www.flyertalk.com/forum/thail...ket-krabi.html

and many many more...

Don't forget to post you plans in http://www.flyertalk.com/forum/thail...er-thread.html and check out before you leave who else will be around. There is usually someone around and willing to get together for a drink.