As a web enthusiast, I've registered with so many sites that I lost account of the number of profiles I maintain (or ought to!). That said, below is my best shot at listing at least the main ones:
Academia.edu
Anime N. Network
Blogger
CouchSurfing
Del.icio.us
DeviantArt
Digg
Facebook
Firefox addons
Flickr
Flixster
FriendFeed
Geni
GoodReads
Google
Google Reader
Hi5
Identi.ca
IMDb
Last.fm
LaunchPad
LibraryThing
LinkedIn
LiveSpaces
MySpace
NetLog
Orkut
Plaxo
Technorati
Twitter
Vimeo
WAYN
Wikimedia
Xing
Youtube