Finding the right set of parameters is quite important in a lot of research - machine learning and computational neuroscience are two fields that I know of. I recently had to ascertain the optimal parameter set for my simulations too. I came up with a quick script to do it for me.
I finally found the time to make myself a business card, and of course, I did it in LaTeX.
Most researchers keep a research journal where we note down our musings, notes and so on. While a paper diary is still quite common, I'd really prefer something on my laptop/computer. There are various applications out there for journal writing, but none of them really match up to good old LaTeX. I've written a simple script that makes it really easy to maintain a journal using LaTeX - Calliope.