TicketMaster
TicketMaster is the primary seller of Ravens tickets. If you can get them through here, you'll get them for the price printed on the ticket (or "face value"). The only problem with TicketMaster is they don't let you look at all the available tickets. They just give you a set and you have to take those or give them up and try again. Very frustrating.
www.ticketmaster.com
TicketLiquidator
TicketLiquidator is the best secondary market seller of Ravens tickets. If you want really great seats or just different seats than you can get on TicketMaster, you'll have to go to a broker like this. They almost always have front row 50-yard-line tickets available, but they're like 2 or 3 times more expensive than TicketMaster. But, since TicketMaster doesn't usually have them available, you usually just have to suck it up and pay the asking price. The flip side is that sometimes you can even get the tickets for LESS than the original selling price if it's not a popular game.
www.ticketliquidator.com