You can find a detailed chart here (along with retailers):
http://xbox-scene.com/modchips4_table.htm
Those are also the current popular chips which work on all xbox versions. I personally would recommend the x-ecuter 3 or x-ecuter 2.6b (for a basic chip). However, there are others here that would equally recommend the other chips.
If you had a ps2 chipped, there is a pretty big difference with the xbox. Mainly the chips functionality. Backup wise, all chips do the exact same thing. They all boot backups directly and can all be turned off for xbox live. However, some may require you to get a radioshack switch for external switches. The ones that do, can be set to be turned on/off with the eject/power button as an alternative to a switch.
The only difference with the chips are bios flash size and hardware addons. Some also have a custom OS. For legal reasons, chips do not come with any hacked bios, so you will need to flash them in order to boot backups.