I like Cryptsy and mcxNOW, they seem to be the most stable for altcoins.
There's also a new one called crypto-trade (see sig for link) which looks really promising, but I haven't really used it properly yet.
K.
I was looking at this one earlier... i really like the layout.
I already use cryptsy and BTC-e, I was just wondering if there are ANY benefits to using one over the other.
I had to use mtgox to get money from US bank into BTC, then transferred BTC to BTC-e... lost alot because of the price difference.