So many good choices. I try to keep things varied just for interest, but the ones I have most commonly are: eggs (every single morning, because they're the easiest to make); chicken (baked two or three times a week at home; possibly more outside); shrimp (once a week); canned tuna, oysters, clams, etc. (frequently — ease of preparation), cashews, peanuts (most days), tofu (not everyone likes it but for me it's convenient boiled two or three times each week), and boneless ribs from my favorite Chinese restaurant (once or twice a week). I also like a good steak (ribeye, or New York strip, medium rare), pork, lamb, and duck (but have these far less often).
Damn... Now I'm hungry....