I've decided I should know at least one language for:
- Server-side web development
- Client-side web development
- Power (fast, efficient)
- Multi-platform usage (deployment, etc)
- Scripting

It's really useful as it means I have a language from pretty much everything. Ruby is one I am trying for server-side web dev and I like it so far; nothing on this Earth will persuade me to use PHP though, it's one hell of an ugly language :P