Current status of cryptographic hash functions as of 2010-01-07
Name Status: Safe, Not safe, Broken
MD2 Not safe
MD4 Broken
MD5 Broken (in particular, look at MD5 considered harmful today and also earlier work for the same group at Colliding X.509 Certificates based on MD5-collisions)
SHA-1 Not safe
SHA-2: SHA-256 Safe
SHA-2: SHA-512 Safe