Please find the below listing of some very useful module that will make the theme developer life easier

1. Sweaver

   Make themes editable by anyone

2. Chaos Tool Suit

   Provides a collection of APIs and tools to assist developers for example ajax, form pop-up

3. Colorbox

   Provides jQuery-based lightbox plugin

4. Theme Developer

   Help the themer to get more information of the page and its content.

5. Views

   Listing of content items

6. Administration Menu

   Provides all the options of the default toolbar and all the menu options without having to navigate through sub-menus.

7. Conditional Stylesheets

   Targeting the browser via the theme's .info file and loading the stylsheets accordingly

8. Devel

   Useful to both module and theme developers

9. @font-your-face

   Facilitate an admin interface for browsing and applying web fonts to your Drupal themes

10. Frontpage

    Provides functionality to assign different front pages for anonymous and authenticated users

11. HTML5 Tools

    Aims to allow Drupal sites to be built using HTML 5

12. .mobi

    Target mobile devices

13. Mobile Theme

    Theme for use with mobile devices

14. Organic Groups

    Makes it easy to control block and content visibility by group

15. Nice Menus

    Provides drop down menus

16. Noggin

    Facilitate to add a custom header image to the default Drupal themes directly from the Theme Manager

17. Panels

    Allows the creation of multi-column layouts.

18. Semantic Views

    Use this views to get rid of unwanted HTML on views template pages

19. Skinr

    Allows theme developer to define a set of reusable CSS styles

20. Style Guide

    Lets you check the styling for your theme

21. Taxonomy Theme

    facilitate to change the theme of a given node based on the taxonomy term or vocabulary

22. ThemeKey

    Advanced theme switcher

23. Webform

    Produce complex and advanced forms directly from within the admin interface

Thanks