In response to Robbie's question -- I buy my ladybugs at our local nursery. A package of 3000 costs me about $8. What I have found is that they need carbohydrates as well as the protein in the aphids. There are a couple ways for them to get it: 1) have something flowering so they can ingest the nectar (my cilantro is going to seed and they love it!) or if you don't have something flowering, put a raisin or 2 in a little dish of water and they will come and drink the "tea". I usually put a couple toothpicks in the raisins so the ladybugs have a way to get their treat but still get out of the dish.
They will fly to the brightest point - like a moth. So you may want to find a way to confine them to keep them around. Eventually they will have babies. YouTube has some interesting videos on the life cycle of ladybugs.