TicketMaster
For a really popular game, you want to try to get your tickets from TicketMaster. They usually sell out in like 15 minutes, but if you go online to order as soon as they go onsale you might get some.
www.ticketmaster.com
TicketLiquidator
If you can't get them through TicketMaster, you can always get them through a broker like TicketLiquidator. Sometimes you just have to pay a lot for a great seat. Of all the brokers on the web, this one consistently has the lowest prices and the best customer service.
www.ticketliquidator.com
E-Bay
E-Bay has a whole ticket section where people can auction off extra seats. Buyer beware, though... there are no guarantees.
www.ebay.com
Craigslist
There aren't a lot of great deals here, and it's hard to deal with some of the sellers because you have to contact them directly.
www.craigslist.com
