If you're a Boston Sports fan, it doesn't get any better than Ace Ticket! They have the largest inventory of area tickets, especially for the Patriots! They have an office near both Fenway Park and the TD Garden too so you can always pick up your tickets at their office on the way to the game. Have done this many times in the past, I go to games for all four area teams every season.
You'll pay a little more than face value but their customer service is excellent and I always know that if a game were cancelled or something happened, they would honor it and issue me a refund. Ace Ticket has been in business for years.