There are obvious 3 char names that have value in any ext ie Mp3, K-9, 4x4, for example.
I have a personal interest in NLL names w/ a "4" prefix or a "1" prex and sufx and have sold a few, in info, biz as wel as .us exts, ie 1ip.biz, in the $100-$200 range. Additionally, I have sold NLN.us, and LLN.info and .biz names for $100-$150. So there is a market there, if not overwhelming.
NLL names that I've gotten some offers and alot of interest in the .com and .net, include 4MD, 4Rx, and 1,2, and 4 combined w/ Mr, IP, RV, ID, Dr, BA, NY, LA, AU, UK, US and a few others. My feeling is that good combinations of 3 char names of this nature, are also worth the investment in the .info/biz/us/selectcctld, as well. I don't expect a quick turnaround on my investment and have, in fact, pruned several out of my portfolio, not because of thinking they wouldn't work out, but due to sheer volume and having "overstocked" in that particular category, and these represent a longer term investment, IMHO.