My most common shell commands:
171 hg 144 fg 77 rm 71 ls 38 cd 28 vi 24 nosetests 17 killall 15 tissue 15 python
I tend to keep Vim open for a long time, running many commands from within it. That's why I don't have lots of task switching like Mike. I learned Emacs before Vim, so blame it on that. I also usually run tests from within Vim; otherwise nosetests would definitely be #1.
Tissue is a ticketing system I've been working on. It's super simple – the whole ticket database is stored in a single plaintext file. The idea is to fit in with DVCSes like Mercurial better. Having a single monolithic Trac instance breaks down when you have dozens of repositories, each of which may have certain tickets fixed or not. By storing the ticket database in a plaintext file within the repository, you get (1) explicit ties between code fixes and ticket changes, and (2) free merging of modified tickets when the corresponding code merge happens. I'm about to switch BitBacker from Trac to this, so it will hopefully get released some time.