Lycox at XDA has designed a skin for HTC Calculator that wors for WVGA devices only. Have a look at its features:

• Fully skinned
• high quality graphics that are made from scratch
• landscape support

Access the skin from the link below.

Via XDA

Want to get rid of the dated look of the WMP skin? Now you can! Just install this WMP12 skin and voila, WMP 10 on your device will look like the WMP12 [link]

If you want something colorful for your HTC, try this skin. ‘Colored Wireless Settings’ skin allows you to customize your icons, color and much more. The skin is created by Antoniomistretta at XDA. 

Via XDA

If you loved the GTX Sense theme and currently run Windows Mobile 6.5 on your phone, you will adore this theme. The skin is only available for VGA resolution devices at the moment but the developer has said they will be coming for other resolutions as well. Install Instructions : Goto Settings -> Personal -> Home -> Items and un-check "Windows Default" Install GTX Titanium.cab Go back to Settings -> Personal -> Home -> Items and re-check "Windows Default" [xda-devs] [...]

How to install:

1- Install Resco Explorer
2- Copy the skin file + pictures (icons) in your Resco Explorer/Skins directory and in resco explorer go to menu/options/customize/skin and choose your preferred skin.

[download here]