I am the biggest disc whore. I buy from all sorts of places.
If I am intersted in a disc I've never had before, I have to buy it from a local vendor. Some place where I can see it and touch it.
When I lived in Cali I bought all my discs from the DTWorld store.
In the area I'm in now, there are established local vendors at two different courses who sell discs from thier cars. Good stuff though, local candy fund plastic and most new releases.
I have recently found the disc racks at the local Play it Again Sports stores, now I look for new branches to rifle through thier inventory.
We have two nice brick and mortar disc golf stores locally as well, with walls full of rare and out of print discs to gaze at. Both also have indoor putting ranges set up, and will gladly let you try out putters until your arm falls off.
The local REI stores now carry discs, mostly premium plastic, and also there is a True Value hardware store in the area that has been stocking Innova and Discraft for at least 10 years now, I buy from them regularily, they have some weights and colors I never see anywhere else, as well as hard to find models, like Eco Xcals and Destroyers.
I recently bought two discs from Spinners Disc Golf in Phoenix, they sure have some sweet stuff there. I will buy a sweet dye job off of Ebay now and then.
If I was looking for CE plastic, I would have to say that Clearwater Disc Golf store mentioned previously has some tasty stuff.
Hero is your best 150 class supplier.
If you know what you want, I dont think anyone makes it easier to buy exactly the right disc than Disc Golf Center, with thier weight and colors all posted online.