The default Windows 7 theme is pretty cool and you can even personalise it by changing the glass colours. In fact there are plenty of cool themes available online for Windows 7. However, sooner or later you are bound to get tired of the default Windows 7 Aero theme and its numerous variations. Fortunately for us, the modding community has already started developing unique Visual Styles for Windows 7. Here are some of the best Windows 7 Themes or Visual Styles (scroll down for installation instructions):
2. Ribbon VS
3. SlanXP 2.0
4. Gel XP Blue
8. Red Ice
11. Leopard OSX
14. Aero Hilled
15. M7 Remix III
19. Soliq 7.1
In order to use the above themes you will need to patch the Windows Themes sub-system. I recommend UxStyle by Rafael for patching the system files. If you are not comfortable with modifying core system files you can use AveStyler (it implements in-memory patch).
Most of the themes are available in ZIP or RAR archives. Extract the theme to C:\Windows\Resources\Themes(where C:\ is the partition with Windows Seven). The .theme file should be reside in the \Themes folder and not in a sub-folder.
Many themes contain additional files such as explorer.exe. You will need to replace the original explorer.exe file (present in C:\Windows directory) with the modded file. There are a couple of ways to do this. Here is the simplest way to do it:
Take ownership of the file.
Rename it to explorer_bak.exe.
Copy-paste the modded explorer.exe file.
Kill explorer.exe using the Task Manager.
Click on File->New Task(Run) and launch explorer.exe.
You can also use Replacer for replacing system files. Although it is no longer under active developement, it still works on most occasions.