in short: don´t go to Thailand for clubbing, isn´t worth it. Enjoy the sightseeing, the beach and the food, but relax from clubbing for a couple of weeks.
"East coast":
Forget Samui for clubbing... there used to be one or two locations in Lamai (for example with Nakadia playing), but they have been closed for two years now. Chaweng had some locations, too, but apart from Mint you only got the GreenMango and the rest of the Reggaeclub... not that much of a choice.
The parties at RockyBay used to be nice, but have been closed down for years now.
Only idea is to go to either Phangan for the FullMoon (won´t go even near there for the last few years, too much beerboys. You thought Amnesia had beerboys? Go to HaadRin...) or head further to Ko Tao. Divers only, but some nice bars to hang out.
for Bangkok: havent been to the RCA, only to Lucifer (almost completely empty two times) and to Narcissus. Narc is a pretty club, but mostly Eurodance and the odd trance record mixed in. Around 90% well-to-do thais, the rest a sprinkling of Expats and travellers. Dress smart! Not traveller style.
The old Ministry of Sound in 2001 was cool and brimming to the top, has unfortunately closed down in 2003 or something.
my 2 cents from our six Thailand trips in the last few years. Great country to really relax.
EDIT: had one of my best parties ever at a private fullmoon party with around 40 ppl from all over the world on Phangan, though. DJ flown in from Birmingham, great sound system, fullmoon, nice ppl... but that was way back in 2000