There are two websites that I recommend. The same group of people created them and they have been great.

Last year I got money back because of their per diem calculator:

1. EZPerDiem.com - Per Diem Tax Rates & The Per Diem Calculator for Flight Crews
2. EZCrewTax.com - Outstanding Flight Crew Tax Preparation

If you use the promo code: C1Q4L when registering, you will save yourself another 10%.