WD are great drives. And the price of a 500 gb drive now is kinda low so its a good time to buy.
I would suggest getting two drives tho if you can afford it. One would be for the OS and programs and the other can be for data and possibly a few game installs if you choose. That way if one goes down you're not completly SOL.
I would even look at an SSD. They'll greatly reduce your loading times.
If you're only going to use one or two magnetic drives, get either a Seagate 7200.12 or a Samsung Spinpoint F3, for performance reasons.
If, however, you're going to get a SSD as your OS/apps drive, capacity becomes more important than speed for the data drive. I'd go for the biggest available within budget from a reputable company like Seagate or WD.