eastoftheweb – this excellent page has several games you can compete against each other in:

• multipopword
• multiswitchword
• multieight

as well as some great single player games:

• eight letters
• popword
• codeword
• definetime
• storyman
• switchword

 gamezone –  here you will find the excellent “Grammar of Doom” game plus a lot of smaller games (click on those labelled intermediate – advanced please, this site caters for primary through to secondary)

 

wordplays.com – this site has links to a number of games:

• Boggler
• Words in a word
• Word morph
• Cryptogram
• Polygon
• Crossword challenge

 

etymologic! – this site claims to be the toughest word game on the web

 

Plus…

There are literally 100’s of links to games HERE. I haven’t sorted them, so some may be dead links, some may be blocked etc, but there is still heaps to be enjoyed here.