I like WinRAR for its built-in parity functionality. You can achieve similar results with 7-Zip using PAR2, but having it built right into WinRAR with two options (add a recovery record to each archive, or create separate recovery archives (basically what PAR2 does)) is so much more convenient.

WinRAR is like what..? 30-35 bucks? That's per user, unlimited machines, lifetime license. More than fair I'd say.