I think Meld is a good gui tool for git diff.
setp 1:Ubuntu install meld
sudo apt-get install meld
step 2:create a shell script named git_meld.sh
vim ~/bin/ngit-meld.sh
#!/bin/sh
meld $2 $5
step 3: chang git_meld.sh permissions
chmod +x ~/bin/git_meld.sh
step 4: config git diff tool
git config --global diff.external ~/bin/git-meld.sh
注意:做个个shell的原因是GIT会送7个参数给Meld,但是Meld只需要两个参数,两个需要比较的文件名。所以不能直接用Meld