I have owned my Sprint Touch Diamond for exactly two years this January. I entered the custom ROM scene thanks for xda-developers.com and ppcgeeks.com.
Unfortunately while the Touch Diamond was cutting edge hardware at the time, the software was notably lacking. I was able to spruce up performance, battery life and functionality by flashing custom ROMs to my device. Though each one I tried was notably lacking. Many ROM “chefs” (developers) prefer to add their own custom flare to their ROMs, whether it be custom images, apps, or settings. But, this is exactly why I flashed away from Sprint's stock ROM full of bloatware images, apps, and settings!
Somewhere along the line I ran into Juicy's series of ROMs which were nearly perfect. Unfortunately Windows Mobile 6.5.x was released and somewhat fragmented Juicy's offerings. I found myself wishing for a perfect stock 6.5 ROM where the ROM scene leaned towards hacking the latest Sense software to work on older devices. This lead to performance issues and worse: broken functions. Since my Diamond is now an end of line device (2 years is a long time to own the same phone), I set out to build my first and final perfect ROM.
The ROM is called Touch Diamond One. It is a solid Windows Mobile 6.5 (build 21725) ROM which is fast, stable, and maintains excellent battery life.
The ROM features the traditional Diamond theme, with mostly stock WM6.5 features and splashes of HTC Sense where appropriate and stable (such as the Notifications, Power Off, Camera, Album, Wi-Fi Router, etc). I also modified the scrollbar to get out of the way since WM6.5 has fairly solid finger scrolling. See the attached screenshots, I feel they speak louder than I.
You can download the ROM here.
More information can be found here, at the pccgeeks.com thread.