I really enjoy camtasia. I'm using right now and memory jumps from 80,000 K to 95,000 K and CPU from 3% - 12% usage.
Just to give you an idea, the higher ends (95,000 K & 12%) are directly related to zooming in and out of a 150 MB panoramic .tif image in photoshop.
For reference, I'm running windows 7 (64-bit) on a core i7 @ 2.8Ghz with ASUS ENGTX 470 (DDR5 1280 MB) and 6GB DDR3 1066.
I was recording full screen (1920x1200).
I've heard good things about Adobe captivate, although I haven't had a chance to test it out. I believe Captivate is significantly more expensive, though, unless you are purchasing only an upgrade.