Starting today Megabus is giving away 200,000 FREE tickets!! It's part of a "green" promotion to keep people from doing holiday travel in their cars, and also a way to help families get together for the holidays. Awww, how nice of them huh? You will still have to pay the 50 cent booking fee, but you can probably dig around in your couch cushions or in your car for that.
The free tickets also depend on how many people book for the same specific bus and location, so if someone else has already grabbed the ticket you want, try changing the departure time or the date and you should still be able to get one. Hurry though! These are expected to be gone by the end of the day!!
I plan on getting one to do a day trip to NYC maybe. We did this last January and LOVED the megabus! It left right from the Back Bay T Station and you can park your car in the garage there, or get street parking if you're lucky. The buses themselves are actually pretty nice - free wifi, plenty of outlets, comfy chairs, and enough room to nap.