All Sold Out
Ticket auction site.
http://www.allsoldout.com/

Aloud.com
Buy tickets online or sign up for the free gig alert service.
http://www.aloud.com/

Broadway
Tickets, theatre and hotel packages, programs and more.
http://www.broadway.com/

Computicket
Tickets for bus rides, cinema shows, live events, sports, themes, festivals, etc.
http://www.computicket.com/

Craig's List
Look under the relevant "For Sale" section for tickets to upcoming events and shows.
http://www.craigslist.org/

Dynamite Ticketz
Online reseller of hard to get tickets.
http://www.dynamiteticketz.com/

Ebay
Snag a ticket online.
http://www.ebay.com/

Keith Prowse
Tickets for theatre, music and arts events, as well attractions, for customers in the US, Canada, UK, Ireland, Australia, New Zealand and many other countries.
http://www.keithprowse.com/

London Theatre Guide
Pick-up theatre tickets at half-price at one of the two TKTS booths in London.
http://www.officiallondontheatre.co.uk/tkts
http://www.tkts.com/index_default.html

NME
Tickets to music gigs in the United Kingdom.
http://www.nme.com/gigs/index.htm

Powergig
Your source for finding and booking college entertainment, corporate entertainment, concerts, wedding entertainment, national stars, famous performers, bands, musicians, comedians, stand-up comics, magicians, public speakers, keynote speakers, motivational speakers, disc jockeys and other performers.
http://www.powergig.com/

Raymond Gubbay
Book tickets to opera, ballet, classical and special events throughout the UK.
http://www.raymondgubbay.co.uk/

Scarlet Mist
Avoid dealing with touts by using this ethical gig and festival ticket exchange site.
http://www.scarletmist.com/

Seatwave
Buy and sell second hand tickets to live events.
http://www.seatwave.com/

See
Online retailer of tickets for theatre shows, gigs, concerts, festivals, exhibitions, sporting events and more.
http://www.seetickets.com/

Stop Tout.com
An ethical ticket exchange that sells tickets strictly at face value.
http://www.stoptout.com/

Stub Hub
Puts ticket hunters in touch with tickets sellers - for a small fee.
http://www.stubhub.com/concert-tickets/

Theatre Development Fund
Purchase tickets to Broadway shows at bargain prices at one of the two TKTS booths in New York.
http://www.tdf.org/
http://www.tkts.com/

Theatre Direct International
TDI is the travel industry's leading provider of information and tickets for Broadway, off-Broadway and West End theatre.
http://www.theatredirect.com/

TickCo
Specializes in the resale of hard to get sports, concert and theatre tickets.
http://www.tickco.com/

Ticketek
Aussie sports and entertainment ticketing operation.
http://premier.ticketek.com.au/
http://www.ticketek.com.au/
http://www.ticketek.com/

Ticketek
Buy online tickets to Kiwi events.
http://premier.ticketek.co.nz/
http://www.ticketek.com/

Ticketfinders International LLC
The company can help you source tickets to football, opera, rock concert, theatre, tennis, motor racing, golf, rugby and boxing events anywhere in the world.
http://www.ticket-finders.com/

Ticketmaster
Well known American ticket seller.
http://www.ticketmaster.com/

Ticketmaster International
For all your ticket buying needs.
http://www.ticketmaster.com/international/

Tickets Online
Tickets for everything from rock and pop concerts to motor racing.
http://www.tickets-online.co.uk/

Tickets.com
International ticket box office.
http://www.tickets.com/

Ticketweb
Online ticket seller with a worldwide presence.
http://www.ticketweb.com/

Tours.com
Online directory of websites selling tickets to theatre shows, sporting events, concerts, tours and cultural events, etc.
http://www.tours.com/tickets.php

Viagogo
Buy and sell tickets at face value.
http://www.viagogo.com/
http://www.viagogo.co.uk/

ViatorBook
Book tickets to attractions, theatres, events, tours and sightseeing worldwide.
http://www.shop.viator.com/

World Entertainment Ticketing Centre
Buy tickets at the click of a button.
http://www.ticketclic.com/