Have booked flights to Bangkok at the end of May and will pick up a rental car at the airport and tour around the central or Issan region for a week or so and then drive to Koh Chang for some beach and diving.
I could use some hotel/bungalow recommendations and advice on the best area to stay on the island. Also, any recommendations for dive centres on the island would be appreciated.
Finally, is it worth stopping at Rayong for a day or two on the way down?

i have booked 4 days on koh chang for june....we settled on the barali after several positive comments here on fodors, especially from travelduo and jamesA.....not sure about diving, but think this is centered in the southern tip of the island....??
i used the www.huahin.20m.com site to make my reservations at about 3550 B/nite inclusive...that is a medium level accomodation--deluxe ocean front i think

Yes there is diving, a lot of the waters are a protected Marine National Park, White Sand Dive center comes up a lot. Probably not as good as Koh Tao but certainly the opportunity to dive.
Entirely up to you but you might think about picking up your rental outside of BKK which saves the hassle of getting through town unless you know Bangkok well. Budget have a very large number of locations. Even after all these years if I go into bangkok I always park at a Mall parking on the outer suburbs and then cab or whatever and then cab back to the mall to pick up the car, I never drive around the city itself. If you are heading north east maybe pick up the car in Nakhon Ratchasima or Khon Kaen, head down from there to Koh Chang and leave the car at Pattaya, just an idea. If not if you get the car delivered to your hotel budget will print you a directions map.

When we were in KC last december we dove the wings dive center. They were really nice and the guy that owns it is a pilot for Bangkok air, and his wife grew up in California so their english is almost as good as mine!

jeffrey---i like your sign language better than your spoken word...haha

WHERE IS THAT REPORT ON SA???????

Thanks for the advice. JamesA - great idea re picking up the car from Khon Kaen - I have usually collected a car from Budget @ the airport and haven't found it a problem getting out of the city to drive down south (but I haven't tried the north yet!) I think we will get the train from Don Muang to Khon Kaen & pick up the car there.
rhkkmk - thanks for the tip on Barali -looks good for the price - I am incline just to turn up and negotiate a rate on arrival as it shouldn't be too busy at that time of year.
Travelduo what was the diving like in KC?

Well the diving want that great, but we were there for loy kratong so it was a full moon which made it kind of merky. my wife and i work in the bahamas and down in belize so thats the kind of diving we are used to and its nothing like that!