Meerkat turns SSH tunnels -- a fairly obscure and complicated concept -- into a feature anyone should be able to use, and does so in a very Mac-like way.
I've known about SSH tunnels for a long time, but I've never been able to get them working. The concept is simple enough: a SSH connection is formed between two computers, allowing for secure access between them. (For more, see SSH: Tunneling Explained.)
What would you use a SSH tunnel for? Here are a couple possibilities: you can stream your iTunes library across the web for free. Our local library has a terribly onerous "web filter" which even blocks Delicious and a bunch of other useful sites. By setting up a SSH tunnel and SOCKS proxy I can avoid that filter. If I want to access my webhosting management panel, I have to do so from a "known" IP address or go through a multi-step process to register another IP. By using a SSH tunnel, I can securely connect to my webhosting company and then access the tunnel.
But how do you setup ssh tunnels? You could do it manually via Terminal.app, but that's not very Mac-like. We've mentioned Meekat before but even then I wasn't able to get it to work until recently. What made the difference? The new "Tunnel Setup Assistant." When version 1.5 was released, it added something very cool, especially for laptop users: automatic reconnection. Combine it with NetworkLocation and you can have a nearly seamless and flexible set of rules to let you access all of your information securely, regardless of where you are. (It's also fully AppleScript-able.)
If you've ever tried to setup a SSH tunnel before and gave up because it was too complicated or too much work, give Meerkat a look. It's a slick program that should appeal to power Mac users of all shades. There's a 14-day demo, plenty of time to figure out how it works and how to use it. A license costs US$19.95, and there's a 30-day guarantee. If you have any questions, I found the developer, Justin Miller, to be very responsive.