If you are using Drupal for one of your website, if you are a developer or a designer using Drupal for your web projects, this collection of Drupal 7 theming resources is for you. If you are starting to learn Drupal, it is also important to get useful resources. This collection also can help you to get useful information easily.
Very helpful article from PINGV about theme in Drupal 7. The comments and responses also very informative.
http://pingv.com/blog/a-peek-at-drupal-7-theme-system-changes There is an update version of presentation after Drupal 7 is released - http://pingv.com/node/132
There is also a presentation that can be download if you have slideshare account.http://www.slideshare.net/laurascott/grok-drupal-7-theming-2011-feb-update. There are other helpful resourecs in their blog http://pingv.com/blog. And this is a beautiful, colorful Drupal site too.
An article of Drupal 7 theming from scratch by Megan McDermott who is co-founder and editor of A Padded Cell and administrator at The Webmaster Forums. This is a step by step tutorial. That is very easy to follow if you have HTML and CSS knowledge and basic knowledge of Drupal setup, theming and Drupal terminology. http://www.apaddedcell.com/how-create-drupal-7-theme-scratch. There is also a download link for the theme files at the end of the tutorial.
Drupal.org, D.O, is the best resource for all the Drupal designers and developers. However it is not easy to get a helpful solution if you don't know where to search.
In Drupal 7, designers can create various customizations -
Here is also a helpful detail documentation about "Theming nodes by content type" and "Working with template suggestions". The most helpful (and yes also need to pay more time to learn) is Theming Guide from D.O
There are so many other Drupal 7 theming tutorials around the web. Just search with Google. If you have some other resources, please drop a link in the comment. The Drupal community always love sharing and will thank you.
If you are still new in Drupal and thinking Drupal is very hard, read this articles about things those stopped our improvements (in Burmese language) or original article from online Marketing Strategist Tommy Walker entitled 106 Excuses That Prevent You From Ever Becoming Great.