- SQL (various dialects)
- Haskell (even though I don't have a strong mathematical background)
- Vala (for Linux development)
- C/C++ (if it can not be avoided ...)
- x86 assembly
At work we mostly develop Windows solutions (with an emphasis on database independency).
I'm using Gentoo and Debian GNU/Linux at home and have extensive Linux knowledge. I also like to play with Debian GNU/Hurd from time to time :).