There are the old Polaroids, of course.
But in recent times Polaroid also started selling the "zero-ink" line of printers and integrated camera/printers, and these are different than the older models. These have an all-digital workflow, the colors in the paper are activated not chemically like the old ones, but thermally (as I understand it). The result is a printed photo that looks like the prints that you get from a lab (less quality though), and there are no white margins around the picture like before. The printer only model can be connected via bluetooth to a cell phone to download photos, or via USB cable to any camera that supports PictBridge (even DSLRs!). This is a huge benefit in my opinion, because you are not limited to a crappy camera like in the old days.
Google "polaroid zero-ink" to see what's available. I have two printers from them, one that prints little 2x3 photos, and one that is less little that prints 3x4s. Both operate on batteries and are intended for taking them out in the field.