GitX is available at https://github.com/brotherbard/gitx/downloads (Get the experimental branch)
Git Tower is available at http://www.git-tower.com/
Textmate has a GIT Bundle at https://github.com/jcf/git-tmbundle (It's quite good, but maybe not for designers).
And Giggle (http://live.gnome.org/giggle).
Windows is the only OS lacking a good client, but I use GitX for Mac every day, as do the less technical "devs" at our Startup.
Git Extensions (http://sourceforge.net/projects/gitextensions/) is actually really, really, good. The UI is well-designed and fast. Wish more people knew about it.
I've been using the whatever default Windows port that is linked from Git's download page for several months bow and there is nothing atrocious about it. It works well and it does differ much from the Linux version. (edit) The command line version that is.
I use TortoiseHG and I expected parity.
Given that git was created for hosting the Linux kernel, it should be obvious why it's not a first-class citizen.
And of course, the command line option through msysgit is great.