I've registered as a breast milk donor with the MothersMilk cooperative. Next step is to get some blood work done. In the mean time I'll be pumping every day. To minimize shipping costs, donations must be at least 150oz. Sounds like a lot, but I've already got roughly 15 oz in 3 pumping sessions. Not too shabby. I estimate it will take me about a month of daily pumping to store enough for my first donation.
Since I bought a good pump, I've never had to worry about my pumping output. With my first, I bought a pump from Target thinking all pumps were created equal. Not so! Even if you plan to use a pump once a month (as I do for the occasional time away from the little one), I highly recommend getting a pump from the recommended list here. They range in price but a decent pump can run about $150. Which is about the average price of pumps you will find on store shelves. These recommended pumps are well worth the investment as it will lessen the likelihood of injury and will get you much more breast milk bang for your buck. I bought the Ameda Purely Yours, and absolutely love it.
If you have to work and pump, I highly recommend browsing www.workandpump.com. There is a wealth of information for working moms or any mom that wants to pump. Even if you pump occasionally, it helps to learn how to get the most out of your pumping sessions. Above all remember, pumping output is NEVER an indication of breast milk supply.