For chains, I've had some good burgers at Five Guys, Jake's Wayback and I'm a big fan of the Red Robin "Royal" with the fried egg. And while I love me a bacon cheeseburger, a couple of my favorites don't include bacon.

For locals, which I prefer:
Ted's Restaurant in Meriden. Definitely a central CT thing, steamed -yep- steamed burgers. Sounds weird but they're great. Stay juicy but the fat gets steamed out. They offer all of the usual toppings but I go with a glop of melted cheddar (to replace the fat lost in the steaming process

), lettuce, tomato and onions. You do have to deal with lines a bit more now that they've been featured on Man vs. Food and Burger Paradise.
Louis' Lunch in New Haven, CT. (Generally) recognized to be the birthplace of the hamburger sandwich in the US. Vertical grilled in their 1898 vintage cast iron grills, served on toast. Only options are cheese, tomato and onion (that's how I get mine) just as it was 100 years ago. No ketchup, no mustard, no mayo, no bacon (which BTW is my favorite food group). The "packaging" really lets the flavor of the beef shine. It's almost like the Soup Nazi's shop on Seinfeld except they're nice folks.