In general:>darker sky and decent cloud separation, slightly smoother skintones:
Deep yellow (2 stops, don't bother with light yellow 1-stop ones)>noticeably dark sky and great cloud separation, very smooth skintones, almost ghostly/porcelain looking skin
Deep red (3 stops).>for rough and gritty, tanned skintones - usually works with men or models with great skin
Green. You'll lose the sky and clouds though, green vegetation noticeably lighter.>general purpose filter with slight but perceptible effect on skies and skintones, as well as vegetation
Yellow-green. Hoya makes nice ones, just 1 stop of light loss (more like 2/3rds of a stop). This is my most used/general purpose one, along with a deep yellow.
Then of course all the usual stuff applies, like polarisers, graduated NDs etc., and those are good for colour too, obviously. You can even get a graduated oranger filter, kinda like an graduated ND but instead of being neutral on the top part it's orange. To compound the effect of gnd+orange for black and white. Kinda gimmicky though.
Also for some fun you can get an infrared filter. R72 (720nm) is nice + some Rollei Infrared film, to experiment with infrared. With film, trying infrared is cheap cause you just need a filter and an IR film, which isn't more expensive than normal panchromatic films.
Lastly, for niche cases, even a deep blue filter can be interesting. If you want to *magnify* haze and mist for a misty look. You'll lose the sky+clouds completely though.