Seriously what ericb said, milk the app store and advertise your apps online if you can, keep it going but the investment climate is lame everywhere. I am now in the same situation where I had 30k cash for the first time with no debt and I essentially put it in a safety deposit box at the bank so I won't spend it. If you look at money market, CD's etc, they all stink right now so just lock it up.

If you have not bought a house yet then I would look into doing that and taking advantage of the 8k tax break for first time home buyers. Sounds like you have enough down payment to cover 20% and get out of the PMI insurance.

You might use that money to hire another developer you can train and crank out more apps, and hit the android market as well.