Ok this is not something that i researched about, but found a list that was prepared by a plugin creator, White Shadow who created the list with the plugins which had the highest downloads.

Here is the list -
1. Michael Torbert
961 306 downloads. Co-author of All In One SEO Pack (originally created by Uberdose).
2. Matt Mullenweg
921 827 downloads. Everybody knows Matt, the main WP dev and author of Akismet.
3. Lester ‘GaMerZ’ Chan
775 220 downloads. Author of WP-Polls and other cool plugins.
4. Arne Brachhold
628 350 downloads. Author of Google XML Sitemaps, etc.
5. Andy Skelton
449 345 downloads. Author of WordPress.com Stats. Another dedicated hacker.
6. Alex Rabe
429 705 downloads. Author of NextGEN Gallery, etc.
7. Oliver Seidel
361 918 downloads. Author of cforms II.
8. Joost de Valk
328 036 downloads. Author of Sociable, Google Analytics for WP and numerous other tools.
9. Donncha O Caoimh
246 752 downloads. Author of WP Super Cache and other assorted plugins.
10. Vladimir Prelovac
244 963 downloads. Author of Smart YouTube, various SEO plugins, and more.

The list has the most downloaded plugins, but there are some other cool plugins too out of the list. I would be reviewing those from the above list that i didn’t use yet. I have used All in One SEO Pack, Sociable, Lester Chan’s plugins and few others.

Btw that was a great list prepared by W-shadow.