Technical Question: Spam comments

Here's a question for the blog-tech savvy: is there any way to stop spam comments in Blogger? I added a "captcha" check to the comment box some weeks ago, but it doesn't seem to have slowed down the spammers at all. Are other people dealing with the same spammers I've been afflicted by?

After two and a half years I'm finally thinking of switching to a different blog service. These days I only have maybe 2 solid hours a week to sit at my blog, and I'd prefer to use that time actually writing!