Although not the latest version, you can get SnagIt 7.2.5 for free:

1. Download the trial version of v7.2.5 from here.
2. Get your key here.
3. After you install it and run it for the first time, click the Unlock link when the SnagIt Message Centre is displayed.

Thanks to Confessions of a freeware junkie for the tip off.

[Update: 2010-09-06] The link to the key in step 2 is now dead. You could consider Screenpresso.