Lansinoh breast milk storage bags are a great way for nursing mothers to store their breastmilk for use by caretakers. The come in packages of 25 and are pre-sterilized 6 ounce zip-top bags.
They are easy to fill and pour from. They are graduated, and easy to write the date on. The zip-top changes color when they have been successfully zipped (I have put a bag of milk on its side in the freezer without having fully zipped it... so this is a nice feature). Occasionally a bag will leak while thawing, but I have yet to run across a brand that does not have this problem from time to time.
The biggest issue I have with this product is the expense. These bags run about $0.30 each. To me this expense is not worth it and I have ended up using a cheaper breastmilk storage bag, or even a high-quality regular zip-top bag with no problems.