An excellent site that is very similar to AQW and Wizard101 is Runescape; the world's most popular free MMORPG with 10 million active users every month and over 150 million registered accounts. The multiplayer game takes place in the medieval fantasy world of Gienlionr, which is divided into hundreds of different regions, cities and kingdoms. Players can interact with each other and each region offers different types of challenges for the players.
A newer and fresher MMORPG site is Dragons Call; a 2D browser game where users choose a character, male or female, to set off on quests to defeat enemies. This interesting game is similar to Wizard101 and I guarantee it will keep you entertained for hours on end.
Another cool site is Club Penguin; a virtual world where users have penguin avatars so they can play games, chat or decorate their igloos. It is recommended for ages 8-14 but does have a number of sections just for paying members.
A few others sites similar to AQW and Wizard1011 that you might like are evony.com, travian.com, tribalwars.com and epicquest.com. All these games are fun and time-consuming so be prepared to get addicted to playing them.