[Pellinore]

The old Gary Gygax written Descent into the Depths of the Earth series (1st edition, can't remember the exact title but it was a long series of linked modules which took you from 1st level up to 14-15th level) were great. I'm sure you can find them somewhere. I haven't tried any 3rd edition or 3.5 stuff so can't comment on that.If you are wanting to write your own scenario then any subterranean creatures will fit.