Virtually anything You want, including X forwarding and any kind of virtual desktop finally *secure*, without sending passwords/traffic in the clear. Or, create encrypted tunnel between two machines, even if one is unreachable (behind NAT, that You don't control, so can't open ports), or even both unreachable, if You use common server in between, Your own (for example, home router with Tomato/OpenWRT/DD-WRT/whatever capable of real ssh), or one available as service (some of them free, google for it).

That was only to name few - it is hard to answer Your question, because it's like "I've got my first computer yesterday, please list neat things that I can do with it. I like playing soceer and basketball, and I'm listening to Heavy Metal". SSH is very wide topic, where only Your invention limit usage*.

/Estel

*Trivia - just half of an hour ago, I used N900 to control CNC machine, via emc2 and linuxbox without monitor. And, of course, I was connected using SSH