I have prepared a summary page on mtDNA haplogroups:http://www.worldfamilies.net/mtDNA.htm
If you are aware of any project or useful resource that isn't listed, please let me know.
If you are having trouble in figuring out how to join a mt Haplogroup project, here are instructions:
1. When you are already inside the FTDNA system:
In your personal FTDNA page is a blue button labelled "join". Click on that button, then scroll to the very bottom of the page - where you should see a listing for mt Haplogroup projects. Select the letter of your haplogroup, then select the specific project, then select a second gray join button which is lower on the page.
Or, if this doesn't work for you - call or email FTDNA and ask them to transfer you into the project (contact info at bottom pf page at www.FamilyTreeDNA.com
2. When you have been tested by National Genegraphic, but haven't joined FTDNA:
You can transfer yourself, your results and your retained sample to Family Tree DNA. Go to your personal NGGP page and look towards the bottom for a small link called "Learn More". Click through the links and eventually you'll join Family Tree DNA. Once you have done that, you'll be able to join the project of your choice, by using the instructions above.
3. If you have not been tested at FTDNA or NGGP, you cannot join a mt haplogroup project at FTDNA. However, do contact the project administrator, as they may have a provision to manually include you. (click the link at the top of this posting to locate the mt Haplogroup projects, which will allow you to track down the project administrator)