For your iPod Touch:
The Phoenix Mars Mission thingie. Gives you two RSS feeds (one for news one for blog) and the weather report on mars. A widget displays the elapsed mission time on mars. I’d like to see this application give us more. Like real time images and possibly the ability to control the Phoenix craft (during time they are otherwise not using it, of course). Here.
NASA Photograph of the Day. This is potentially cool. When I went to look at it the first time, it was the lamest photograph I’ve ever seen from NASA. (The street somewhere around the Smithsonian with people waking around and stuff.) But this could be fun. Here.