I use many different email accounts and programs for various reasons professionally and personally:
Gmail - Integrated with Google reader, documents, calendar and chat. Great mail search ability.
Hotmail - 5GB free storage, and it's integrated with all of my other Microsoft ID's / gamer tags.
Yahoo - Spam receptacle, it is where all the Spam gets sent to.
AOL - Netscape was my first account I have 2 accounts I maintain associated with home and work
Inbox - 5GB free storage, great organizer for calendar, photos, documents
GMX - complete stand alone solution separate from an active Internet browser. Secure with 1GB free storage.
HotPop - pop3 only service that is received into my client - Thunderbird
I have them all going into one client - Thunderbird where I also have my RSS news feeds going to.
Configured so I can see them all at once organized in their respective provider named folders at a glance.
If I get bored with Thunderbird 2.0.0.19, then I would use any of my hot standbys: Evolution, Eudora 8.0.0 Beta 4, Outlook or Outlook Express.