Bangkok - Kho Pha Ngan info

I have a faur bit of info on Phangan in the first link below. I wont suggest particular places because it depends on your individual preferences. There is also a sublink in the link list top right of page to losing-touch's Backpacking in Thailand which has good Phangan info - l.t. (Brent) is a bit of a Phangan specialist. He has also got a good section on Bangkok stays.
I kinda like the area between the river pier and KSR - this 3 or 4 block section has a number of quiet streets with good value hotels and guest houses - Bella Bella GH is one of several.

=) Well, you really need to let us know what your budget is. As for getting there, make sure you avoid those damn tourist buses on KSR. Lomprayah is the exception to this rule. The southern bus terminal is not too far away if you are keen on the whole bus idea. The advantage of Lomprayah is that you will get in an hour before the masses arrive. For me, the train is the way to go. Check out http://www.seat61.com/Thailand.htm for some really good info.

In Bangkok, you will probably want to stay in the KSR area. It will be convenient for your purposes.

I cannot advise regarding Koh Phangan because of the aforementioned budget problem. I can tell you where I stay is Cookies Bungalow. Also, what will you be doing there? Do you want to party every night, or do you want to just chill out on the beach?

Hat Rin is where you want to be if you want to party, but outside full moon period the beach and area gets very quiet. If the full moon is not your scene, then I recommend Hat Khom, either Coral Bay or Coconut Beach, about 300-500baht a night but decent rooms and good resorts. Hat Khom has a great beach for snorkelling, and you can take a boat to the 'Bottle Beach' next door. Not alot to do here though aside from sit on the beach, swim in the sea, or chill in your resort. I headed there after the full moon party and it was fantastic to chill out for a few days.

if you are travelling alone i do NOT recommend bottle beach. it's completely boring. if you want a nice combination of beautiful beach and peace if you want it, but with some nightlife and social activities when you want it- go to thong nai pan or had yao on koh phangan.