You can setup a gui merge tool for resolving 3-way merge situations, e.g. merge conflicts.

Windows

Go to http://www.perforce.com/downloads
Browse by Component | Clients | Visual Merge Tool
Download and install the appropriate installer.

In your ~/.gitconfig add:

[merge]
    tool = p4tool
[mergetool "p4tool"]
    cmd = \"/c/Program Files/Perforce/p4merge.exe\" \"$BASE\" \"$LOCAL\" \"$REMOTE\" \"$MERGED\"
    keepBackup = false
[mergetool]
    prompt = false

Linux

TBD