I have spent the last hour or so looking into focusing screens for the 7D as I was, until recently, under the impression that you could not change it.
Once I found out it was possible my mind immediately jumped to whether I could get a micro prism FS like the one I LOVE in the FTb, and sure enough, after a good search I finally found what I was looking for!
I had looked through split screens, matte screens, micro prisms and mixes of all the above but finally decided that all I wanted was a micro prism.
There were many good posts on forums and a few different options, I even had a look on eBay but decided against it.
In the end the best option seemed to be a screen from KatzEye which always got consistently gleaming reviews but seemed a little pricey at $105.00 + shipping from the US (I live in the UK), and an extra $55 if you wanted some treatment on it to make it brighter...
But then I found the wonderful focusingscreen.com (I know, how did I not find this first time...) which would appear to be based in Taiwan. It offers multiple types of screens for a multitude of cameras (even Nikon screens for Canon!) and has a brilliant page to explain all the types of screen as well as what they look like while focusing in real life! In addition to all of the above they also have installation guides, with photos, for so many cameras...
Really wish I had found this site first off, and maybe I should have but maybe someone else will find this useful!
Prices are a bit cheaper than KatzEye, and I get the impression they modify screens rather than produce their own but I could be completely wrong in this assumption.
Will post my thoughts when I get it!