I second the vote for 5 Guys. There's a few around town I believe, but I've had good luck with the one on Elizabeth. Great burgers for cheep, and all the shell peanuts you can eat while you wait for your food.
1. Adeleta's Fine Mexican Food in Loveland. Really popular, so get a reservation and enjoy.
2. The Rib House in Longmont has the best Kansas BBQ I've ever had.
3. Rock Bottom Brewery is awesome too...anything with good beer!