Blogs
Teencentral - http://www.teencentral.net
A blog where you can ask question or for help with all different kinds of topics.
Grief - http://www.newhope-grief.org/teengrief/memory06.html
To help in the grieving process, this site has a portion in which you can add a short memorial.
Partner abuse - http://www.scarleteen.com/forum/Forum29/HTML/000027.html
You can ask your questions and they are answered from someone who has survived an abusive relationship. Along with this topic this site addresses other questions of sexual nature in a frank non judgmental environment.
MySpace - http://myspace.com/
A website where teens can post and create there own space that others can view and comment on.
AOL communities - http://dmoz.org/Kids_and_Teens/Teen_Life/Online_Communities/
This site has links for teen on all different topics of interest. Anything from writing, games, music and even politics.
Diary Land - http://www.diaryland.com/
Diary land is geared toward the younger teen. This site is free and you can keep a journal online.
E Blogger - http://www.blogger.com/start/
A great site for those that have not blogged before. This site will walk you through the steps.
Wikis
Wikispaces : wikis for every one - http://www.wikispaces.com/
This site is a free website that offers a place for you to create your own wiki.
Media Wiki - http://www.mediawiki.org/wiki/MediaWiki
This link is to a site that has the software needed for wikis. It is the same software used by wikipedia.