Avent Isis Breast Pump
Even though I use a double electric at home, this is what I use at work. Originally I used this at home and used the electric at work, but I can express just as much, just as quickly with a hand pump, plus I don't need an outlet or battery pack, and it takes much less of my precious break time to set up. Replacement parts are cheap and easy to find at major retailers, so if it starts to become inefficient, just replace the plastic valves.
For mothers that breastfeed - this is an essential item! This manual pump is by far the top of its class and is worth its price. It's so easy to clean, store, and travel with. The soft massage cushion is a dream, and the effective suction means less pumping. (This is an important feature for those that are afraid of over-production.) This manual pump was a saviour when I arrived home with my newborn daughter and was suffering from engorgement - no pain and was incredibly effective. I reccomend this pump for any mother that is breastfeeding and needs to occasionally pump or needs to express while travelling.
This was the most comfortable, effective manual pump I used. The pump emulates the suckling of the baby and the suction cup is designed to stimulate the flow of milk. Also, considering how effective it is, $50 is very cheap. If you pick this up, buy the Avent microwave sterilizer I recommended as well. The pump fits in there, making it easy to clean and sterilize.