(in no particular order)
1) Fresh garlic chopped in large pieces. The frozen cubes, any variation of garlic in spice form and even fresh garlic when its diced real small are a problem, in my opinion, because the flavor cooks off by the time your ready serve.
2) Bakenfleish [cheek meat] is far and away the best meat that I have had experience with. It gets so tender and it basically falls apart after cooking it for a few hours in a cholent. The flavor is excellent. Some people go with a pepper crusted pastrami. Personally, I'm not a fan. The pepper messes with the overall flavor and the meat gets weird after cooking overnight. YMMV.
3) Soak the beans overnight beforehand to "soak out the flatulence" as my brother says. Or leave out beans all together. Keep in mind that if you have less beans, or none at all, the water level will be higher than you'd expect. Beans absorb water.
4) Sausage. Kielbasa, to be exact, is my sausage of choice because it, unlike most sausages and hot dogs, doesn't dry out in a cholent and become a piece of rubber. The kielbasa gives the cholent better flavor and is a cool element that kids and the young at heart will enjoy.
5) Lawry's Seasoned Salt and Sweet Chili Sauce. Copious amounts of the former; 2 tablespoons of the latter. You won't be disappointed.
6) Best-kept cholent secret of the modern hippie generation: Sweet Potato. A small one chopped up. Gives the cholent good color and surprisingly good flavor. Don't take my word for it. Try it on a weekend when your alone or have a small crowd. Or, make a small cholent on Thursday night and try it then. YMMV but this idea is like Starwood points: Under-appreciated by most.