Disposable Email Services
A good way to prevent your main email address from being spammed is not using it when creating web accounts or subscribing to websites. Managing different email accounts isn't trivial and dropping a free account when it starts being spammed to open another one in the next minute isn't really usefull either.
What you really need is a temporary email address you can use to prove you're not a robot. One you can throw away as soon as you have used it. That's what disposable email services are for.
If you give Web sites and new contacts a disposable email address instead of your real one, you can selectively disable a disposable address as soon as you get spam through it, but continue using all other aliases. Disposable email address services provide this basic functionality, but some have other neat features that make life with email less spam and more fun.
From About.com: Top 10 Disposable Email Address Services
From Listible.Com: 40 resources on Dispoable Email Services