I bought mine here: http://stores.ebay.com/Amys-Ketapang-Inc
the leaves were very fragrant, clean, and had no rips at all. They were very well packaged. The banana leaves are supposedly better as a healing agent, the primary use of IAL is for breeding and to mimic the betta's natural water conditions. I would get some of each.
Personally I keep on hand:
Aquarium/kosher salt - for fin damage and open wounds
Epsom salt - for stubborn bloating and constipation
Methylene blue - disinfectant, I would use it on severe cuts and injured fish whose immune systems have been compromised
Praziquantel (Jungle's Parasite Clear) - internal parasites
API's Triple Sulfa - broad spectrum antibiotic
Maracyn I - gram positive bacteria
Maracyn II - gram negative bacteria
Malachite Green - severe external parasite infestation (ich/velvet)
CLEAN WATER & REGULAR MAINTENANCE - EVERYTHING :) If you take care of your fish properly, you should not have to worry about him or her getting sick. Do not undervalue the benefits of good care habits. You should regularly test your water with a liquid freshwater master test kit to be sure that your routine is working.