I wish there was an opposite analog to the right-side notifications drawer that came up on the left side that let you have real widgets (Kill off DashBoard) that looked nicer and integrated better. Be neat if it could be built by a third party, could intercept the two finger gesture when done from the left side instead, and could have widgets built with the same combination of HTML, CSS and JavaScript with some system accessing API's like Dashboard and Konfabulator had.
Though in reality, I also wish someone would create a video player with the ability to play anything that could sit in the corner of the screen like a picture-in-picture that was click-through and when the mouse got near it, it could go partially transparent and would never get in the way, but would stay on screen when switching between Fullscreen and spaces. It's my dream video player. Bonus points if it could act as a window to another space or application. Then you wouldn't need it to be a video player, but could have it "looking at" a video player. It would have a menubar presence to configure it and turn it off an on.
It's completely possible. Bowtie has shown that apps can be set to show up on any screen, including FS windows, and float on top of everything else. If I were to teach myself how to program Cocoa, this is the first app I would make. Literally. I would branch off VLC, rip out the extra stuff, give it an always-on-top show-on-every-display option and a menubar presence. It would be my most wanted application for Lion/Mountain Lion.