Polaroid here as well. Then I take the print, tape it to the film holder and write on it the exposure, date and time. Helps me keep track. If I take two shots (same exposure) I process the side without polaroid taped to it first.
Matt's Photo Site "I invent nothing, I rediscover". Auguste Rodin
Some people use some kind of expensive electric Lite-Brite thing that fits on the back of a LF camera and plugs into the wall, but we don't talk about that here.
For formats not amenable to Polaroid, some people have done things like using monobath development for quick proofing or B&W to proof color. This was a common technique at one time in furniture studios, where they would shoot room setups in 11x14".