I've made a TrackBack Ping Bookmarklet for Firefox -- and mine actually works! Others I've seen don't use the "post" method, which is required by the TrackBack specification. Here's my TrackBack Ping Bookmarklet. Drag it to your toolbar. Select the URL to which you want to send a TrackBack Ping, then click the Bookmarklet. Fill in your blog information, and click the button. TODO: Add a method to pull your blog information from the TrackBack RDF you should have on your permalink page.
I made a couple of modifications to the Writeback Plus plugin for Blosxom. Here's the diff file. Basically, I wanted to have the ability to have alternative writebacks display with a shaded background. In addition, I fixed the removal of the builtin trackback flavour. And I also fixed the annoying always plural usage of "writebacks" (i.e., "1 writebacks") -- the method was taken from Pollxn.