How to Select Cryptographic Key Size?
A good article offering guidelines for the determination of key sizes for symmetric cryptosystems, RSA, and discrete logarithm based cryptosystems both over finite fields and over groups of elliptic curves over prime fields.
It can be downloaded here.
Aloha!
Another really good paper/report is the ECRYPT II Yearly Report on Algorithms and Keylengths. Last updated in the autumn 2011 and provides up to date key size comparisons and more.
http://www.ecrypt.eu.org/