My team and I just launched are building Crypto Street -- a meta-exchange for bitcoin, litecoin, PPcoin, and namecoin.  Complete market depth and order books across a few different exchanges to provide initial liquidity (and arbitrage for the early adopters). We should be launching early May, but you can get in the queue by creating a free account at http://www.crypto.st.

We'd love your feedback as we build and launch.