A thread at Stack Overflow explains how to configure git behind a corporate proxy:
git config --global http.proxy http://login:password@our-proxy-server:8088
It’s important to note that if your login has a backslash, as in domain\login, the you must escape the backslash, as in:
git config --global http.proxy http://domain\\\login:password@our-proxy-server:8088
Note the use of three blackslashes.

That’s a great point, thanks. What’s the right syntax if your password has @ in it? I tried escaping it with a \ as well as double \, but that was not successful.
Two suggestions:
1) Change your password
or
2) Use Cntlm. I recently became a fan of Cntlm for two reasons: a) I don’t like storing my password in clear text, especially in mutiple places, which I have to do now for all the different applications on my machine that need to access my corporate proxy; b) some simple applications aren’t don’t even have built-in support for proxy authentication. I generated an encrypted version of my password once for Cntlm to connect to my corporate proxy, and now I just point all my apps to my local Cntlm proxy and they don’t need to worry about proxy authentication.
Seems cntlm has a bug when working with https.
http://stackoverflow.com/questions/6345104/proxy-through-cntlm-why-git-clone-hangs