I find it convenient to include current SCM data before my regular Bash prompt (reduces the chance of “accidents”). Perhaps someone else will find it useful too.

function prompt-pre-exec() {
    repo_root=$(hg root 2>/dev/null)
    if [ -e CVS ]; then
        scm=":: cvs ::"

    elif [ -e .svn ]; then
        scm=":: svn : ${prompt_hl}r$(svn info | grep Revision | sed s/.*:\ //)${prompt_n} ($(svn info | grep Date | sed s/.*\(\//)"

    elif [ -e .gitignore ]; then
        repo_branch=`git branch --no-color 2> /dev/null | sed -e /^[^*]/d -e s/* \(.*\)/\1#/`
        scm=`git show --pretty="format: : git : ${prompt_hl}${repo_branch}%h${prompt_n} : %an, %cr\n:: %s\n" | head -n 2`

    elif [ x != "x$repo_root" ]; then
        repo_cs=$(hg id -i)
        scm=`hg log --template " : hg : ${repo_root##*/} : ${prompt_hl}${repo_cs}${prompt_n} {tags} : {author|user}, {date|age} ago\n:: {desc|firstline|strip}\n" -r ${repo_cs%%+}`

    if [ "x$scm" != x ]; then
        # Trailing \n characters dont seem to expanded 
    export scm    

if [ x"$-" = "xhimBH" ]; then
  # Execute the following function before displaying the prompt
  export PROMPT_COMMAND=prompt-pre-exec

  # Use \[ and \] to exclude the color code from the line wrapping calculations 
  export PS1=${scm}[\@] \u@\h \[${prompt_hl}\]\w #\[${prompt_n}\] 

Then to add color, simply define prompt_hl and prompt_n. I use

export prompt_n="^[^E[00m^]"      # Default color
export prompt_hl="^[^E[01;32m^]"  # Highlight codes

To enter ^[ in emacs, type Ctrl-q then Ctrl-[. Likewise ^E is Ctrl-q Ctrl-e.