I can never remember physics formulae off the top of my head. When I prepared for my PhD candidacy exam I decided to make a formula sheet containing everything. Now, I just have trouble remembering where to look ☺.
My formula sheet is heavily skewed toward Statistical & Thermal Physics and Quantum Mechanics (my favourites), and skimps on Electromagnetism (my, uhh, not as favourite). I also have a sheet specific to Quantum Mechanics with slightly clearer labels below.
These formula sheets are licensed cc-by-nc-sa-3.0.
Or, even better, send me an updated, expanded, or improved pdf ☺.