listen to silverback. buy some sevin liquid concentrate. add 3 oz per gallon of water and use the mix in a spray bottle of your choice. i started treating my plants in early june and haven't needed to use it since late july.
Neem should work great, pretty much anything labeled for aphids should (if used properly.) The trick with organic oils is to continually reapply them. They mess with the molting process of the insects. You can't expect results after one application. Personally, I like to alternate weekly sprays between ER's Zero Tolerance and Neem oil.
Im not sure if i over fertalized or used neem during high heat but my plants are showing either yellowing at center, or general browning/dying of the leaves.
Ive used neem at least 3-4 times over 2 months... Nothing.