The last post in this thread is over 60 days old. Posting in this thread will be considered a bump, so please make an attempt to be courteous if you go ahead with it.
If the last post is over 6 months old, it may instead be a better idea to start a new topic. If you aren't sure about what to do, feel free to ask a staff member for help, or try to locate a 'general questions'-type thread if it exists in this (sub-)forum.
I don't really like making favourites lists, but I'll mention a few that haven't been looked at much yet.
Within a Deep Forest: Surprised nobody mentioned this yet... well-designed and challenging platforming with really nice ambient music. You play as a bouncing ball, adding a whole other mechanic to manage.
Knytt and Knytt Stories: More exploration-based than WaDF, you're a little thing that can jump and climb walls. Knytt Stories also allows one to create their own levels and stories, and you can download those made by others to play as well, why haven't I done this yet... Nifflas' games page.
La-Mulana: Amazingly well-designed, oozing genuine style both macabre and oldschool, filled with a dark story and genuinely challenging riddles and puzzles the likes of which I've never seen before.
Iji: Well I made the thread for it >_>
The Underside: It will be awesome when it's finished and you know it