These are simple sites that enable people to share short pieces of information, some in all formats. That is video,mp3, jpeg and all that. These are more of realtime streams, that many people have embraced.
And they Are?
TWITTER.com
FRIENDFEED.com
PLURK.com
IDENT.ca
GOOGLEBUZZ.com
BRIGHTLITE.com
MEEMI.com
SPOTJOTS.com
well you can as well try them out and see which one suits you. I think twitter leads all.