Remember the days when you had to stand in line all night to get the tickets you want? Now you just have to have the fastest Internet connection (or enough cash to go to a broker).
The place to purchase tickets. Online, charge-by-phone or in person at the TM Center (some restrictive rules apply during high interest events). Search by venue, state or event. Also offering tickets for events in many foreign countries.
Another great site to purchase tickets for entertainment events.
This is a great site if you want to attend theatre in London. They provide tickets for dramas, comedies and plenty of other shows.
Search eBay for sporting tickets using their tickets and experience finder or just enter team names, sporting venues or specific events in their normal search engine. Sometimes this is the cheapest option, because you can make your own bid on the price of tickets.
Here's a site that specializes in Las Vegas and Broadway show tickets. If you want to buy show tickets in advance, it'll be worth your while to shop here.