MotionDSP just shipped version 2.0 of its vReveal software, and if you use a Flip or similar camcorder, it's the cheapest way to reduce shake and improve your video. The previous version of vReveal got great reviews, but it could only handle SD video, which made it useless for the new generation of HD camcorders unless you reduced your footage's resolution down to SD before using the software. Version 2.0 now supports HD in and out. The free version of vReveal 2.0 can only output at 480p maximum, but the premium version with 1080p out will set you back all of $39 (US).
Both versions include image stabilization, contrast and white balance adjustment, sharpening and video filters. The premium version can up-rez SD footage to 720 or 1080p, and can clean up video noise, especially from footage shot with digital zoom or in low light. Both versions greatly benefit from having a CUDA-compatible nVidia graphics card or GPU for application acceleration, but they work fine (just more slowly) without it. Also, vReveal is a Windows-only app, so OS X users are out of luck.
If you're using a higher-end camcorder, you probably don't need the features of vReveal or already have better software, but if you're using a Flip, Creative Vado, Sony or Samsung Flip clone and you have a Windows PC, the $39 that you pay for vReveal 2.0 could be the best investment in video quality improvement that you'll ever make.