The likely problem is this:
Someone that you know, has your e-Mail address in their address book system (what ever that may be.) And their system was either snagged by an mail scavenger, or turned into a mail bot-net. The third common form is for a mailing list that you are on (commercial or not) to have sold ($) that list which ends up in the hands of spammers.
Outside of your control, your e-Mail address is used by this other system to send e-Mail using these addresses (including yours) for spamming purposes. This makes the spam mail look somewhat legitimate because it is using real from & to addresses.
There is little that you can do, except to block your own address (which probably is counter productive) or have your mail filtered through very savvy heuristics. The practical problem is that the way that your e-Mail address is used is a moving target and it becomes a nightmare for a computer to deal with it well.
Now, on the bright side, usually these come and go in waves. Meaning that the issue for you is hot right now, but the problem will subside. Then it may reoccur.
To try to stem this problem in the future, you should have an e-Mail alias (or separate address) for mailing lists, one for on-line shopping and one for personal friends only. This would at least allow you to intelligently understand what avenue was compromised and would also allow you to kill a troubled account with a little less pain.
-Alan