As someone linked to earlier, I wrote an article about what I bought with my $50 credit on teleread.
http://www.teleread.org/blog/?p=6922
The problem with almost all the titles suggested (mostly good by the way) is that you can buy print versions almost always for cheaper than the ebook versions.
I think the Paris Review anthology is probably the best buy I made...although that too was available for cheaper as a print book.
I think when the NAEB mobipocket reader comes, there will a lot more choices. also, the new .epub format will improve the selection somewhat.