Depends on what you are after.
Kuta beach (just north of the airport) is the main "resort area" with the largest amount of cheap accomodation, bars etc. If you're looking for a cheap and cheerful, fun, beach break then head for here .. it's supposed to have the best beach on the island too.
If you want to splash out a bit on a fancy resort there are loads to choose from .. most are in Sanur (on the South East Cost ) or Nusa Dua (at the very southern tip of the island).. I think you can find some really fancy places and (certainly used to be the case in not so busy periods) you can get some great deals if you just turn up and haggle. Be warned though while many of these places are lovely they are the kind of place you would not leave for the week or whatever - quite in the middle of nowhere with not a lot of stuff around them ... not my cup of tea but many people like it.
What I liked best was inland up in the hills ... Ubud was a very nice town with good range of accomodation and plenty of things to do ... I certainly preferred this to the beach resorty places .. but it's a question of what you're after - don't go here if you want to lie on the beach (it's a good distance from the beach)
[broken link removed] is a pretty good site