The finalists of the Extend Firefox Contest have been announced on Mozilla's site. The list also gives links to install the chosen extansions. I use/have used 10 of the 18 extensions listed there.
We are happy to announce the finalists in our Extend Firefox Contest, a contest held to award the best and brightest extension developers in the Firefox community. The contest asked entrants to create Firefox Extensions that are innovative, useful, and integrate with today's Web services. Over 200 Extensions were submitted to the contest. Many thanks to everyone who entered and everyone who helped spread the word about the contest.
Extend Firefox Contest Finalists :: Mozilla Update