If fantasy baseball and baseball cards got together and had offspring it would be this, Topps BUNT. You build a fantasy team of nine players made up of nine virtual cards. Then depending on how well the players are doing those cards rise in value. The game is designed to be massively social, your total score is constantly being put up on a leaderboard to show you how well you're doing compared to others in your area. It's from those leaderboards you can also interact with other fans and try to trade cards or players. Topps BUNT is right now an iPad only app though it is free.
Minds of Modern Mathematics
If Math-letes - so to speak - are more your thing, then a new one from IBM called Minds of Modern Mathematics may be of interest. It's an interactive timeline from the year 1000 through to the 60s designed to show how math has played a role in nearly every human innovation, everything from art to technology. Slide from side to side clicking on the hundreds of mathematicians and events to get more information. It's actually a digital version of 50-foot-long real world, physical timeline created for the 1964 World's Fair by Charles and Ray Eames. In addition to the information you can click through, there are also a handful of those 60s videos designed to teach some really complex math concepts to very non-mathematical minds. Minds of Modern Mathematics is also an iPad-only app and also free.