I took some time this weekend to upgrade my wife's MacBook Pro 15-inch and hooked her up with two essential upgrades that give the MBP the best of both worlds.
First, I removed the stock 500GB hard drive -- which was a dog -- and replaced it with a scorching-fast 480GB Mercury Extreme Pro SSD from OWC. The Extreme Pro SSD is the best upgrade that I've ever installed in a MacBook Pro because it was like instantly doubling its speed. I couldn't put it in my 13-inch MacBook Air, so my wife's the lucky recipient. 240GB costs $395, 480GB will set you back $860.
Second, I yanked the stock optical drive -- which practically had cobwebs in it -- and replaced it with an OptiBay Drive Kit from MCE Technologies. The OptiBay costs $99 blank (or $199 with a 1TB hard drive) and gets you a whole second drive worth of internal storage inside your MBP. Opting for the 1TB OptiBay offsets some of the pricey storage you might have to sacrifice by going with a SSD as your primary drive.
Two great upgrades that are essential for the MacBook Pro.