First, from Lilia Efimova — the Waypath plguin (for both Radio and Movable Type) that lets you show possibly related links from other blogs. It apparently identifies text strings in the current post and attempts to match them to others in the blogosphere. I haven’t played with it yet, but it strikes me as something that would have significant benefits as part of a k-log.
Second, from Jenny Levine — two add-ins to your weblog that will notify you by AIM that someone’s at your site (and even tell you who they are and how to IM them if they’ve shared that info) and another that will present blog-friendly traffic analysis. I tested out the AIM notification and it worked perfectly. (Possible applications: private websites where you want to engage visitors. A consultant would do well to use this kind of service to provide rapid access to clients.)