Windows 1.0

Windows 2.0

Windows 3.0

Windows 3.11

Windows 3.11 for Workgroups

Windows 95

Windows 98

Windows ME

Windows 2000

Windows XP

Windows Vista

 Source: Wired News

1. UI
2. Flip 3D
3. Live Thumbnails
4. ReadyBoost
5. Cool Performance Tools
6. Better Security
7. Search
8. Software Gadgets
9. Wireless Networking
10. Network Map
11. Better Graphics With Windows Photo Gallery
12. Enhanced Windows Movie Maker
13. Better Notebook Support
14. File Sharing and Syncing
15. Parental Controls

Find them all and the details around each of those items here