According to Tuaw and Mobilecrunch, you can earn rewards for installing apps at apperang.com (google it if you want to know more). Few useful paid apps for free daily + real rewards. Believe me, it works well (with Firefox :P)
If you find it useful, please register with my referal :beer::
There is a similar apprebates.com, but my payment has delayed for 2 days already and verification process is more complex. Not sure about them.