in Kendall Square:
The Blue Room
Also in Kendall is Legal Seafoods. Someone will probably recommend it to you. It sucks. I mean, it really is horrid. If you go, stick with oysters, chowder or the most simple piece of grilled fish. Don't bother with anything else.
In Central Square:
If you need a lot of space, you can always go to Sidney's at the Hotel @ MIT. Standard, bland hotel food, but the service is good and the atmosphere is highly conducive to working meals.
Casual, but solid meals (better for lunches):
Middlesex lounge on Mass Ave heading towards Central Square - good pressed sandwiches, soups, salads
Miracle of Science just a bit further up for really good, slightly upscale bar food
Quick list of some of my faves in that neighborhood:
Rendezvous - wonderful food. try to do the Sunday night prix fixe
Salts - small, friendsly, excellent French inspired meals.
East Coast Grill - always has an interesting menu. Fish is terrific and so is the BBQ. A place that can really please everyone. Great cocktails and specials. Love the raw bar.
Emma's Pizza - casual and comfy. Great selection of thin crust pizzas. Salads are pretty good too.
Blue Room - I've never had a bad meal here. Brunch buffet is pretty interesting.
Many, many good options. I still haven't been to some of the ones listed above, but I have enjoyed Helmand (upscale Afghan), the Similans (Westernized but good Thai), Rendezvous (upscale American), Anise (Chowhound-polarizing upscale Szechuan food), Emma's (my favorite pizza in Cambridge/Somerville), and B-Side Lounge (if you want to go downscale with drinks and tasty, fun-to-eat items like baked gouda in a skillet).
I want to second the recommendation for Blue Room - it is a favorite and certainly not a studenty place. Great food and atmosphere.
Since you are posting on Chowhound I will assume are a little adventurous and might want to check out Anise, which is directly across from Blue Room in Kendall Square. As others have posted here the Sichuan cuisine there is excellent - a little different than your usual Chinese restaurant.
Helmand is also a favorite in the vicinity, though it's a bit of a walk from Kendall. I am not a fan of Helmand myself but a lot of others are, so probably worth the trip.