Making beer & brats involves boiling bratwurst & sliced onions in beer and finishing the brats on the grill.
What's a good beer to use to cook with and then drink with the brats once they're done?
Go for lower alcohol and less hoppy. Alcoholic drinks on meat can give great flavor, but the alcohol has a tendency to dry out said meat. Some form of malty session beer would be great to cook with, if you had any near you. Rauchbier would probably work well, since that smoke flavor would really enhance the meat, but drinking it with it might be too much. If you do cook them this way, don't boil, just simmer for a while.
What would probably be pretty pimp, would be to make a beer reduction with the onions and serve that on the brats. Sauté some onions, and right after they've started to caramelize, add some of a great malty beer...maybe a Marzen... and simmer it on medium heat until it starts to thicken up and make a syrupy sauce that sticks to the onions.
When cooking sweeter meats like brats or other sausages, I always use very malty beers, typically of the darker variety. Nut brown ales, dopplebock, stouts are favorites.
Flank steak marinated in a combo of Newcastle Brown Ale, lots of red pepper flakes, garlic, lime juice, salt and pepper makes universally awesome fajita meat.
If you're making sauces or deglazing a pan, definitely go with the malty stuff.