I don't personally recommend straying from o-cha if you're starting out. There's is some of the best at the best prices. Matcha quality can diminish in the hands of US vendors (Rishi).
However, there are a few other options if you are trying to buy from a Vendor in the states. Joel, a fellow matcha enthusiasts, has good thins to say about Ito En's teas, so you might try them.
Den's Tea is another Japanese company located here in the US, but they have a very limited selection of matcha.
There is also Matcha Source, but they are a reseller, so you pay more than you would if you simply purchased it from the original Japanese vendor.
There are certain missconceptions about matcha and quality; I think the closer you can get to the source, matcha produced by people who know what they are doing, the better the quality and price (O-cha, Hibiki an, Ippodo, and such).