The cheapest, but best software that might suit your needs is ScreenFlick by Ariellum.
http://www.araelium.com/screenflick
$29. Basically, you'd set your recording area around what you want to record, hit record and within 5 seconds it starts recording. It will also record sound.
I used to use it to record my game reviews off of my SlingBox as it streamed to my iMac, until I got a Haupague HDPVR and EyeTV.
I will warn you, however, if you are recording your own shows or something similar, the RAW movie files can get VERY LARGE. At least a GB/hour at a smallish-medium resolution. At the resolutions I used to record my games at (1280x720 720p) it was more like 3 GB/45 mins or so.
It is updated fairly frequently, and the program now shows a little green bar when opened if there is an update ready to be installed.
Hitting 'start recording' gives you the movie-style 5 second countdown then it begins recording. To stop recording hit shift+command+2. You can also pre-set the maximum frames per second to record at before recording.
After recording, just hit the export button and it will export to a small variety of file formats. You can also preview the recorded movies before you export them. However, to delete the RAW files, you have to hit the delete key in the lower left of the movies panel while highlighting the RAW movie to delete (the delete button looks like a - ). After that, you will have to quit (fully quit, command+Q while in the program, or right click/control click the icon in your dock and select quit) the program before you can actually empty it from the trash (otherwise OS X will say it is still in use by ScreenFlick).
Exporting can actually take longer than it took to record, so be aware of that. Also, before deleting the RAW file, play it when it appears in QuickTime Player, to ensure the sound and such stayed synced (normally only an issue for longer files).