The search engine Clusty has created Clusty Clouds (check out the side bar to the right for an example). It's an interesting feature that makes it easy to generate tag clouds for particular key-phrases...the ones you frequently see on blogs. It took me about two seconds to create my final pick.
Clusty was designed from the ground up as a clustering engine (it's actually vivisimo (http://vivisimo.com/). Here's how they describe it:-
A Clusty Cloud is a tool that webmasters or bloggers can use to instantly visualize a topic using the familiar tag cloud display. What makes the Clusty Cloud unique is that you can create a cloud based on any topic or query - you don't need tags or months of content on a subject to create an interesting cloud.
Clusty Clouds are generated using our search results for the topic you enter. Since the tags you see come from Clusty, you can click on any of them to go to Clusty's search results. Using Clusty to generate the cloud also ensures that it is always up-to-date because the clusters are generated in real-time.
Why not check it out for your blog?