http://www.lastminute.com/theme-parks – All the big names in one place – you can buy tickets for Alton Towers, Chessington World of Adventures, Thorpe Park, Legoland Windsor, Drayton Manor, Diggerland, Camelot & Lightwater Valley. Lastminute.com also have lots of other great ideas for days out such as The London Eye. They can also sell tickets for Euro Disney, Asterix Land, & Port Aventura.