I don't know that many updos. My favorite updo is the French Twist (Roll). It only takes a couple of Good Hair Days pins to hold it up and it always looks good, even when it's not perfect. It is a classy style and can be worn casually too. I always get compliments with this style.
My other favorite is a side bun which always looks great and turns heads too. I usually braid my buns which is very easy to do and just pin it under.
All updos can be enhanced (as was mentioned) with accessories like flowers, ribbons, barrettes, etc.