Darwin's has this vaguely hipster/organic vibe going on -- it's a market but also has a counter where they'll make sandwiches, etc. I liked their (somewhat) eclectic selection, and the sandwich was definitely a winner.
I had terrific chocolate chip pancakes here one Sunday morning. The decor is cute and retro-diner-y, which really does it for me. A little on the pricier side, but it's worth it if you go with friends.
What's not to like about the Field? It's not super-duper-loud, so you can actually have a conversation with people. They have a good selection of beer on tap, and there's a pool table if the mood strikes.
Honestly, Stefani's is a lot like Cinderella's (a bit further up Mass Ave). They have pizza, though I personally think they make a pretty great sub. Reasonably cheap, too -- so, comfort food when you need it, I suppose.
You get what you pay for, or so they say. I've only been to Salt's once: the service was exceptional, the rolls were delicious, and the ambiance was just right. I was personally a little underwhelmed by the entrees that we tried, but I think that's sort of hit-or-miss. Their duck is supposedly incredible, but you have to call ahead to get it.
Basically your standard cookie-cutter Irish pub/restaurant. A full menu with reasonable entrees, a good selection of beers and liquors. Trivia night on Tuesday is always fun, in my opinion.
La Luna Caffe (now "Cafe Luna") is one of my favorite spots to go to early on Sunday, for a cup of coffee and a breakfast sandwich. The people are friendly and the coffee is great. Even better: live music several nights a week -- jazz in particular. I highly recommend it.
The terrific Italian restaurant that doesn't look like one. Order at the counter (no table service), but be wowed by generous portions that are also quite tasty. Definitely a lot of bang for the buck. You're not coming here for the decor, though.
It's hard to argue with the convenience of Libby's, or really with the selection -- they likely have what you're looking for. It's very much a get in, get what you need, get out kind of place.
It's certainly cheap and the decor is crazy. The jam was good, the omelet I had isn't something I will write home about. I imagine it's much more fun to go here with a group of your friends, rather than alone, so keep that in mind; I'd go principally for the ambiance and cheap food than for a terrific meal.