Here are some websites for practicing English above B2 level:

For an overview of the English Verb system: Verbs

For many exercises to practice grammar: Grammar
(the above site has much more English in their left sidebar on this page)

Dave's ESL Cafe has a lot of grammar (and help): Dave'sESL

For many lessons and activities for more advanced learners: ESOLcourse

For many reading, listening and pronuciation exercises: Manythings

For grammar, videos and listening exercises: 4esl

Learn English with the BBC news: BBCnews

Skillswise teaches everday reading, writing and listening: Skillswise

The British Council site for learners: BritCouncil

Advanced site with idioms, phrasal verbs and more: UseEnglish

For college or academic English: PurdueOwl

Improve your pronunciation with good practical videos: Sozoexchange

Over 1,700 lessons based on news stories with listening : Breakingnews

Advanced listening lessons: Adlisten

Goos pronunciation page: Pronounce

Listening, vocabulary and video lessons: ESLlab

Englishclub's site also has good links and advice at bottom of homepage: ESL

Links to many pages for listening (some with texts): TESLlinks

Language games for advanced learners: ESLgames

Audio books and songs to read and listen to: EslBits

Many advanced lessons on Youtube: Youtube