One of the best bits of value I get from the various (and diverse) domains I own is that when I sign-up for something, and the procedure requires an email address, – well, I just go and create one: just for whoever's asking (and, let's face it, most everyone does require a valid email address these days (I wonder why!))
It's really useful when used this way - for two reasons:
1. You can just remove your 'used' address after you've been 'verified'
2. You can monitor the email sent to it, and see exactly who's selling their client's email addresses (and then you can delete it!)
Of course, you can buy a domain (no, you don't need a webserver – or anything really) from a myriad of places on the Interweb. Me, well I use www.123-reg.com for all of mine. Mainly, I suppose, because I used them for the first one. However, they're cheap, they offer unlimited email-forwarding, and – lastly – they always use females in their graphics (shallow – me?!)
Anyway, a good way to avoid spam is to invest in a domain name!