We download Wordpress Themes for various reasons, either to use completely as a Blog skin or to take small elements from each to develop our own personalized site. As is the open source nature of the Wordpress Comunity, this has helped Wordpress become the number one Blogging CMS.
Below are a list of my Top Thirty Wordpress Themes that have helped me, in one way or the other.
Note: Any themes you feel I have forgotten post them in the comments at the bottom of the page.

1. Zeke 1.0

Zeke 1.0Website: solostream.com
Author: Solo Stream.

2. Bus Full of Hippies

A Bus Full Of HippiesWebsite: http://archgfx.net
Author: John Oxton.

3. Illacrimo

JS BoxWebsite: http://www.lifespy.com
Author: Lifespy.

4. Plainbox v1.0

JS BoxWebsite: http://jsbox.net/332
Author: Jay Kwong.

5. Artuell

ArtuellWebsite: blog.artueel.be
Author: Erlend Debast.

6. Vengeance

VengeanceWebsite: wpdesigner.com
Author: Small Potato.

7. Merdeka

MerdekaWebsite: ikram-zidane.com
Author: Ikram Zidane.

8. Far From Fearless

Far From FearlessWebsite: farfromfearless.com/
Author: Chris Murphy

9. Salmon

SalmonWebsite: justinshattuck.com
Author: Justin Shattuck

10. Minyx

MinyxWebsite: infectedfx.net
Author: Infected Fx

11. Bogart

BogartWebsite: http://jimmitchell.org
Author: Jim Mitchell

12. Grid Focus

Grid FocusWebsite: 5thirtyone.com
Author: Derek Punsalan

13. Excentric Paradise

Excentric ParadiseWebsite: excentricparadise.de
Author: Excentric Paradise

14. Tweak V.1

TweakWebsite: tweakcast.com
Author: Fall Out Media

15. Tarski

TarskiWebsite: tarskitheme.com
Author: Ben Eastaugh & Chris Sternal-Johnson

16. Cleaker 2.1

Cleaker 2.1Website: pomomusings.com
Author: Adam Walker Cleaveland

17. Autumn Concept

Autumn ConceptWebsite: edmerritt.com
Author: Ed Merrit

18. Xenoria

XenoriaWebsite: nuwen.com
Author: http://nuwen.com

19. Simplicity Bright / Dark

SimplicityWebsite: koch-werkstatt.de
Author: Koch Werstatt

20. Cold Blue

Cold BlueWebsite: webrevolutionary.com
Author: WebRevolutionary

21. Mezzo

MezzoWebsite: wpthemesplugin.com
Author: Moses Francis

22. XV

XVWebsite: blog.unnerkrunt.de
Author: http://blog.unnerkrunt.de/

23. Hemingway

HemingwayWebsite: warpspire.com
Author: Kyle Neath

24. Foliage

FoliageWebsite: /5thirtyone.com
Author: Derek Punsalan

25. Greenery

GreeneryWebsite: ilemoned.com
Author: http://www.ilemoned.com/

26. StripedPlus 1.0

StripedPlus 1.0 Website: theundersigned.net
Author: http://theundersigned.net

27. Pro 2

Pro 2Website: eisabainyo.net
Author: http://eisabainyo.net

28. Marki

MarkiWebsite: ikram-zidane.com
Author: Ikram Zidane

29. Blogging Pro

Blogging ProWebsite: bloggingpro.com

30. Vertigo Squared

Vertigo SquaredWebsite: briangardner.com
Author: Brian Gardner