There are various community websites available, but the main advantage with Yahoo Groups is the integration with email. I mean, you can participate in discussion just by email and there is no need to visit Yahoo Groups website.
Recently, Facebook has also added this email discussion feature in their forums. I recently experimented with it and found this feature similar to Yahoo Groups. Keeping it in mind I have created a Vedic Astrology discussion forum on Facebook. If you are already a member of Facebook, you can request joining.
For Facebook addicts, I think this will be more convenient than Yahoo Groups. Please try experimenting and let me know your feedback. Here is the URL again - http://www.facebook.com/home.php?sk=group_157922590915148&ap=1
Related Forums/ Groups:
Apart from above, if you are looking for system specific forums, here are those -