If you want to venture out of the typical city limits you can ride the Greenline to Coolidge Corner (Brookline) where there are some small stores and some cool places to eat such as Zaftigs, JP Licks (also one on Newbury), Fugokyou, Ana's (as previously mentioned), Finale (dessert joint, also one downtown Boston).
You can ride the Redline I believe to Harvard Square where there are shops (Urban Outfitters, the Coop, GAP, Tannery, American Apparel, EMS, City Sports, Newbury Comics, Adidas) and eats. If you like Mexican food the best Mexican joint EVER is in Harvard Square, The Border Cafe. Be prepared to wait but the food is INSANE and the margaritas are stellar.
Stay away from Central Square Cambridge, its dirty and tons of homeless people.