There are some color-specific staples like demonic tutor, which is used in just about any black deck of quality. Probably the staply-est staples are sol ring and mana crypt if you can afford it, since they go amazingly in virtually every deck ever. Getting a good collection of multicolor generating lands is good too...duals if you're rolling in dough, or my personal budget favorites, the ravnica block bounce lands. mana accelerants and tutors are usually good staples, as are good draw engines like mind's eye and necropotence. Personally one of my favorites is jushi apprentice...the slower format and general lack of instant-speed targeted removal makes him an solid card-advantage generator early, and an easy alt wincon with reliquary tower (minamo, school at water's edge helps too). There's a top 50 card list in the stickies for each color, which is sometimes helpful...it's usually a good idea to look through it when you're making a new deck, although some choices are more deck specific than others.