Like games? Card games are very fun and simple to implement, or simple text games like Russian Roulette, one of my faves. (Update: pay no attention to that sadist below!)
Like sports? Learn how to automate getting articles/stats/feeds off the web on a favorite team/player.
Like technology? Learn about networking, sockets, cool SMS/email tricks.
Like music? Learn how to organize mp3s by their tags, make apps that make customizable playlists or stream music over a network connection.
Like the web? Learn how to make a basic home page with dynamic content, using CGI and the like. Make a "super" Facebook page.