Better dictionaries in the future -- Merriam is terrible for both English and French-English since it's lacking in words. It'd be nice if we could instantly "click" and look up a word in the definition as well.
Better highlighting/note-taking features -- I really like the one they have for the Sony readers where you can circle words or underline text. Highlighting is nice, but I like a little variations sometimes for different types of notes.
Option to adjust the contrast for .PDF and .CBS files -- since the "text" is sometimes too light to read.
A way to tell whether or not a book has been "shelved" -- This is one of my biggest pet-peeve, especially if I'm adding several books at once.
Option to set a Default Dictionary -- I'd like to set the French-English dictionary as my default one when reading French books
Scrolling down page for of .cbz files when in landscape mode - it's easier to read text for graphic novels when I put it in landscape mode but it won't let me scroll to the bottom half of the page. Whenever I try to do so, it just flips to the top half of the next page. It seems to work when I zoom it a bit, but that defeats the whole purpose of having the option to fit the page across the screen since it means I'll have to scroll both left/right and up/down to read everything.