To have your current branch name in your bash prompt, just add this code into .bash_profile file from your home directory.
hgBranch ()
{
if [ -d .hg ]; then
printf "$1" "$(hg branch)"
fi
}
export PS1='${USER}@${HOSTNAME}:\w$(hgBranch " [\033[1;31m(%s)\033[0m]")$ '
Ofcourse, after you edit .bash_profile, you must logout and login again to see the changes.
//later edit
If you want to have the same feature in the graphical terminal, you should add the code above in the .bashrc file.
//2nd later edit
You can find a good “how to” for git on LeaseWeb Labs.