Here's a variant of the Colemak layout that I recently made in Ukelele. It's in the Mac .keylayout format — if anyone knows how to convert to something Windows-friendly please let me know!
A little background: I type a lot of accented letters. Back in my unenlightened days of QWERTY, I used the US Extended layout which ships with Mac OS. I found this very intuitive to use and extremely quick to learn. I still haven't been able to get comfortable with Colemak's option-key inputs after 7 months of learning.
In this variant: everything is the same in the normal input mode. If you hold down Option while pressing keys, however, you'll get the US Extended style input (that is, with the characters rearranged to be in Colemak order). See picture:
Red = dead key. For example, pressing Option-e-a yields á
So, for example: in the US Extended layout, pressing Option-s would enter ß. In this layout, the ß has been moved to the Colemak position so that pressing Option-s still yields ß.
If you type special characters in Colemak (more than just one to two languages), I highly recommend trying this layout. With the US Extended keys you can write in pretty much any Latin-based script (Vietnamese, maybe not!). Most of the "Option" inputs correspond to characters which look similar or are related to the normal input character for that key:
Option-r = ®
Option-1 = ¡
Option-y = ¥
Option-f = ƒ
Option-o = ø
Anyway, I hope this is helpful to someone! Enjoy.