What about the
eSlick? It's basically a Cybook, but it runs the foxit reader, so I guess the pdf support will be quite well handed. Apart from PDF and txt, it's not going to support any other format when it ships in March, but they are working on ereader now, which I think no other device supports, and apparently epub is on their plans.
Regarding Sony, PRS 505 has already been in the market for more than one year. Last year the 700 was launched, which is not actually a real menace, they can coexist, but I'm afraid next year Sony will move on to a new 510 or something, so I would recommend you a different brand (
Sony's infamous internal timer could also be an issue xD).