I would also shill one of the APL derivatives. I've gone from a happy Python dev to a die hard k/q guy very quickly. These languages completely change the way you approach a problem.
It's just a shame that q isn't free for commerical use (though it's free for personal use) and there aren't many jobs outside of finance.
I didn't see your reply before I brought up APL and J here. I've tried k several times, but I always fall back on J, then APL, and then k. I think it's personal bias, since I found J first. I like the symbols of APL as I like mathematical formulas, and now that Dyalog has adopted some J-isms, I've been trying reimplement my J stuff in Dyalog APL. Also Roger Hui of J fame is a Dyalog user too. I thought I would gravitate to k because of my Lisp background, but J is sticking with me.
They are certainly very well known still in my experience I find a lot of people who haven't done C or any lisp before specially people who arent coming from CS backgroud
It's just a shame that q isn't free for commerical use (though it's free for personal use) and there aren't many jobs outside of finance.