Here are a couple fun sites to get you playing around with numbers.
Curious Math is a page full of math tricks and techniques. The entries are brief enough to go through in a few minutes and many are quite useful. For example, see this entry on multiplying two three-digit numbers or this post on multiplying up to 20x20. If you're looking for more, check out the forum.
Inner Algebra is a free Ebook that shows you how to solve equations in your head using techniques such as visualization, chunking and windowing. A lot of seasoned math geeks, for whom these processes are second-nature, might find it interesting to see the steps written out as a method. Anyone taking a standardized test in the near future (GMAT, SATs) could benefit from these time-saving techniques.
Lastly, if you've never gone before, visit math geek mecca: Wolfram's MathWorld. In addition to information on dozens of topics from Geometry to Topology, MathWorld has a classroom with a bunch of learning modules. Be sure to also check out Recreational Mathematics.
These material all make me nostalgic for math camp...Did I say math camp? I meant quarterback camp.
See these animated GIFs from Wolfram's MathWorld.