1.
Runescape is a free online action and adventure game where you can send messages,kill monsters,cook,sell stuff that you make,blacksmith,steal money and it even has some pvp action click
HERE to go to runescape.com

2.
Miniclip is a website that is mostly made for 7-12 year olds but anyone can play it.It has approximately 350 game options,and is not blocked in most schools...you what i'm thinking?
3.
Frugooscape is a fun online game,just like runescape but 10X easier to lvl up and bows don't need arrows,as well as the ability to turn off chat
filters.filters, duel people anywhere, and the ability to put in item codes like..... ::pickup 4747 1 (::pickup=pick up) (4747= item code) (1=item qty)
4..yet another website is funorb it has single-player and pvp(player vs. player) games,it was just made by jagex(the creators of runescape) a few weeks ago,so we can be expecting many more games for that website in the future.Don't get me wrong,it has about 15 games right now,and is still growing,if you have a runescape username,use that to login to funorb...if you don't then make an account on the website,which you can also use on runescape.
5.Adventure quest is a free on-line game with pvp and is just like runescape,except more educational...errrr....I'm learning again!!!