A lot is going to depend on what you need encryption for...

I'll 2nd the vote for Schneier's book; you can get yourself into a lot of trouble if you're using encryption without knowing what you're doing.

A false sense of security could be the least of your worries...

If you're looking for encryption of IP communications, though, OpenSSL (and OpenSSH for telnet-like applications) are widely used. OpenSSL also comes with some general-purpose crypto routines you can adapt to whatever purpose you need.
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Mike