Buy the unit with the lowest possible memory from Apple. Then go to any of the reputable memory dealers online (I use 18004memory) and MAX your ram. The Apple Tax on ram is sick.
The hard drive is also taxed rather heavily, but you will either have to upgrade it yourself or pay someone to do it for you, so it's your call as to whether to get a 7200 or put one in yourself. You'll like having a larger hard drive, and I believe the 500gb's are now availble in 7200 rpm. I know a LOT of people that went for the 320gb's back when the 500's were only available in 5400rpm. (for boot camp speed mainly)
You should think hard as to whether or not you want a 17". If you're going to do be doing graphics work, it can benefit you greatly. I personally would never consider a 17" over my 15" since portability is a very important aspect for me, but for you, screen size may be one of the biggest considerations. If you're going to be using it over 90% of the time sitting on your desk plugged into a 27" flatpanel however, that may not be an issue for you. If you expect to be doing work while mobile with any frequency, while onsite with a client, or need to for example get work done while on a flight, you'd be crazy not to get a 17.
