As the others have said, Lulu is one of the better ones.
- NaomiM
<Added>However, they do have a number of add-ons that push up the cost. I would just go for the basic package that supplies an ISBN number. With that a reader can order your book from any bookshop (although it won't physically be stocked by the bookshops).
I believe Amazon have now hooked up with their own PoD publisher (I have a feeling it's the one linked to HarperCollins' Authonomy website) and will not list Lulu titles, so probably something worth checking out.