Ruby or Python is good. Just pick one. Flip a coin. Or do what I did: I picked the one that _Why's book was about, and that proved to be a very amusing way to choose:
http://poignantguide.net/ruby/
(See also: http://hacketyhack.net/ and http://shoooes.net/ .)
Also good, but for different things: Scheme (as learned from SICP), C, Objective C, Java (so that you'll know what everyone else is complaining about).
Some suggestions:
Rich media websites? Flash/Actionscript
"Desktop-class" web apps? Cappucino or SproutCore
Business web apps? Java or C#, SQL
Aiming to work at a startup? Rails/Ruby or PHP, SQL
Desktop apps? Objective-C or .NET, SQL
Looking to expand your mind? Erlang, Lisp, Haskell, or OCaml
Hardware or Operating Systems? C, C++
Hope that helps. This is by no means a complete (or even totally accurate) list, so others please jump in.
All too many developers think they know what there is to know about both of them, and most of them are wrong.
These are languages that will be useful to you in any shop in the industry; in fact you've probably had occasion to use them both already.
SQL and Javascript. You may think you know them already. But they both reward in-depth study.
Personally, I made a choice between learning Ruby and Python based mostly on emotion: I found most Python code samples more aesthetically pleasing.
Liking it a lot, plus have already written an app and deployed it in the GAE, which is pretty cool in itself