The Tower of English

http://towerofenglish.com/vocabulary.html

The Tower of English is a portal to English learning websites.

Strengths
It has a large number of sites listed, of varying interest and quality, but there is certain to be something for everyone.

Weaknesses
Unfortunately, links at the top of the page take you out of the site to a Google page, rather than being links within the list of vocabulary sites on the page. This is a bit confusing.