I vary it, but this is one that always worked well for me:
1 large onion, chopped
1 can tomato paste
2 stalks celery, diced
garlic, chopped (i use half a head, use whatever you like)
habanero, chopped (whatever you can handle)
1 lb ground lamb
1 lb ground beef (lean, the lamb will supply the fat)
1 bottle of any beer you like to drink
Salt
Pepper
Juice of a lime
Cilantro
Touch of cinnamon
(all to taste, and definitely experiment with the seasonings, this is a good base recipe)
On med-high, add some peanut oil to a pot and cook the celery, habanero, garlic, and onions until the onions start to turn translucent. Don't burn the garlic. Add the tomato paste and combine. Cook it a little until it combines.
Now add the meat and brown it. Don't drain off the fat (unless there's a lot, but remember, lean beef!). Once everything is combined and browned, add the beer and seasonings. Lower the heat (low/med-low) and simmer for as long as you want. It's better the more you let it cook down.
When you serve it, toss in some dark chocolate in the bowl and melt it in. Not everybody likes it, so I don't put it in the base recipe, but it's pretty good to me. Worth a taste at least once.
This recipe's a good base to expand on too. I use pinto beans sometimes, corn other times, vegetables that I have to use up, etc. Just remember that it'll be acidic with the tomato paste and the lime, so adding some starch or serving over rice is really good too.
EDIT: Funboy's post reminded me. Hot breakfast sausage is a great replacement for the lamb. Just hold off on salting it until you taste, as most of the stuff out there is pretty salty.