Free Advice on Adding Tags to a Blog
At the risk of starting to sound like Steve Rubel's blog (hey, who am I kidding!), I just found another service called Tagyu from Adam Kelsey that suggests tags for your posts.
He also offers it as a plug in for those of you that blog from Movebale Type.
In his blog Kalsey invites developers to make their own tools using Tagyu. If someone makes something that works with Blogger, let me know.