It's important to find a pump that best mimics your baby's natural suck
strength and cycle. You can rent a hospital-grade pump for top strength
and efficiency. (You can usually pump both breasts at the same time,
reducing pumping time at work.) If you don't have access to an
electrical outlet where you'll be pumping, a hand pump might be your
best bet. Other factors to consider are the size of the pump
(especially if you have to carry it to and from home every day), how
noisy the motor is and, of course, how easy it is to use. Many moms
leave their larger pump at the office and bring only the attachments
that need to be cleaned to and from work. Others also buy a hand pump
if they need to be out of the office occasionally for meetings or go on
overnight business trips. Some of the latest double electrical pumps:

Avent ISIS iQ DUO (www.aventamerica.com, $350) An electronic "brain"
memorizes the unique suction and speed set by a pumping mom, which can
be adjusted as often as she likes; whisper-quiet motor; easily usable
as a manual pump.

Lansinoh Double Electric Breast Pump
(www.lansinoh.com, $150)  Adjustable suction and speed; quiet motor that doesn't scream "I'm
pumping here!"

Evenflo Elan Breast Pump (www.evenflo.com, $120)
Adjustable speed and vacuum settings; a timer that lets you keep track
of how long you've pumped each session; a dividable bag that allows you
to keep a portion at work.

*Storing and Using Milk Store milk in hard-sided plastic or glass
containers or high-quality sterilized breast-milk bags. Regular plastic
bags can be used for short-term storage (less than 72 hours) but may
leak. Freeze milk in two-ounce portions (a covered ice cube tray works
great) to match what babies generally take at each feeding. This
reduces unnecessary thawing and wasted milk. Clearly mark each bottle
with the date it is pumped. Never heat milk in a microwave or on a
stovetop, because these methods can cause scald spots and will destroy
antibodies. Instead, gently swirl a bottle in warm water. Leave milk at
room temperature for up to eight hours, in an insulated cooler bag for
24 hours, in a refrigerator for up to five days or in the freezer (in
the back) from two weeks to 12 months, depending on the type of
freezer, how often it's opened and its temperature. Discard leftover
milk.   

Source: Academy of Breastfeeding Medicine