I just checked the extensive list of nifty add-ons from Google Labs to enhance your Gmail experience. I was very impresses - it certainly grew from the last time I checked - which was about a year ago or so. I added a few including:
1. Late night math solver
2. Wrong Bob - email the right person
3. Unsending an email - opps solver
4. Attaching images as a context of the email
So which ones have you added and why?