If you know of something that should be listed here, don't forget to tell me...
kdedict by Matthias Kiefer: cgi script to store standard translations in a database and make it available via the web (there's also a demo available).
Flexicon by Logi Ragnarsson: a database of words, each with an assigned language and description.
An index of on-line dictionaries is being maintained at www.facstaff.bucknell.edu/rbeard/diction.html.
Finally a tip: in the German team they are not using their mailing list but a web forum for discussing difficult translations (one term per thread) which has the advantages: (1) that everybody can jump in without a need to subscribe to a mailing list (2) and everything is pretty good documented and easy to find for translators to come. -- The program they are using is Discus, and the German forum is at www.dtp-service.com/discus_d/, check it out. Of course, there are zillions of other programs of that sort.