I'm fond of PVB, as anyone who's read my posts here may have noticed. Prints with similar settings to plain PLA, but can be smoothed with isopropyl alcohol, and smoothed prints can be pretty close to truly transparent if that's your thing. Also, smoothed prints have much improved interlayer adhesion, for obvious reasons.

I've printed a couple of spools of PETG at this point, and it's touchier than PLA, but still easier than the ABS/ASA/HIPS family plastics. In particular, it likes to be stringy, so you need to either tune your retraction or do a certain amount of postprocessing on prints to get uniformly smooth surfaces (I mostly settle for the latter, and "good enough").

I also have a spool of PCL (filament with a very low printing temperature) that I keep meaning to get around to playing with. What can I say? It was on sale. (I buy mostly from filaments.ca , who often have somewhat exotic plastics among their house brand filaments, although they can never seem to keep them in stock. Just as well, since it keeps me from impulse-buying LLDPE or the like.)