Kem cards are the finest playing cards available, they are made of thermo-plastic materials that are virtually tear-proof and washable. These cards will last for years. A little dear but worth it.
COPAG 100% Plastic Playing Cards are great too and somewhat cheaper.
Torcello pvc playing cards again are a very good and will last a very long time.
If all these are a bit too expensive as IrishDave has suggested the bee playing cards are a good quality and inexpensive choice. But I think its worth spending that little extra, you can really notice the difference.