I have been testing parallels with a number of trading/charting apps, and so far it has been great. I am running the new v3.0, but 2.x was just fine also.
Button Trader
QuoteTracker
NinjaTrader
AmiBroker
TWS
Sierra
DTN iQ
MB Trading
Schwab Street Smart Pro
I might add it's nice to see TWS has a OSX friendly app for my IB account, just incase the windows environment would screw the pooch. I run that on a 2nd Mac. I would also note the TWS app doesn't require an Intel Mac, so that also leaves some nice options to run on older, yet still nicely performing Macs.
One big step for OSX/Intel Macs would be one or more of the direct DATA providers to offer OSX friendly software. However, I suppose it's kind of the "chicken or the egg" scenario of which comes 1st... apps or data. Can't have one without the other.
There are a couple of OSX options I might note...
AutoTrader
AlphaTrade (data feed & limited charting)
I'm sure there are more, but I haven't really looked since getting parallels up and running with the apps mentioned above.
Still, I'd love to see folks mention more OSX options if they exist.