I've just added a Swiki to this blog, which is a customised, trainable search engine. Produced by Eurekster (a kiwi company!) it's a community based approach to searching, a portion of which can be embedded in your website.

When you create a Swiki, you create it for a topic, like ASP.NET. From this, a "buzz cloud" is created of keywords that people have used based on this topic, but most importantly, ranks the search results based on what others selected when they performed the search! So, all the good results will filter to the top of the pile. But also, as other people search in your topic area with new keywords, the "buzz cloud" will change, meaning that you can see what's hot and what's not within your topic.

Make sense? ... they have a better explanation on their site . Either way, check it and create your Swiki!