Well being from Maryland, there are a lot of local Maryland brews I like, some of which I believe can be bought nationwide.
Pretty much everything brewed by Clipper City Brewing Co.- I especially like the Heavy Seas line of beers. My favorite is Small Craft Warning. They call it an "Uber Pils"
http://www.ccbeer.com
I also like Flying Dog. I believe they are headquartered out of Co, but they have a brewery here in Frederick. One of my good friends apprenticed here. He's the head brewer at one of our local microbrews now
My favorite Flying Dog is Old Scratch, an Amber Lager
http://www.flyingdogales.com
And then here in Frederick we have 2 microbrews-Barley and Hops and Brewers Alley. I LOVE both. They have EXCELLENT food and EXCELLENT beers. Barley and Hops is kind of in an out of the way locale, so DH and I dont go there that much, but when we DO go out to eat, we usually end up at Brewers Alley. Its in downtown Frederick which is SO much fun. We lived there for 4 years before moving out to the sticks. We used to live only about 2 blocks away from Brewer's-so meh. Plus you can go there, get an appetizer and a FABULOUS wood fired pizza for around $20 for 2 people! Every once in a while the brew a Smoked Porter, its EXCELLENT!
As far as nationally known beers, I gotta love me some Guiness. Its the Irish blood in me I guess LOL! And if its cheap Im looking for, I cant go wrong with the PBR. Please no one blast me for that. PBR rocks!