What sort of support is there out in the wild for non-official cameras which are supported by or compatible with the Raspberry Pi, with or without use of the special interfaces?
There is an entire page on elinux.org that has a list of supported cameras, complete with hardware IDs, operating system, resolutions, whether it needs a powered hub etc. It also has a list of a few to avoid. Here is a screenshot of one small bit:
Lots of USB cameras work fine.
Some like the Logitech C920 even encode to H.264 which helps to push extra pixels through the USB interface