Originally Posted by trophynuts
for files that you download on your phone you can use this awesome app
that some dude made
And I just updated this past weekend!
Note: not many folks know that it will also (in addition to calculating various checksums):
1. verify the contents of a signed jar-type file (.apk, signed ROM or update.zip, etc.) without needing to know any of the checksums (they are already built-in to signed files)
2. perform a verification of your Nandroid backup (custom recoveries do this anyway before a restore is allowed, but you can do it manually outside of ClockworkMod).