This site has been up and down a few times. It's been up for the last few months with no problem, but BMW is working hard to shut them down. Basically the site has copied an entire BMW ETK disc and hosted it online.
FYI: for the time being, the information is pretty accurate, but note that as time progresses it will become outdated as BMW frequently supercedes numbers. For up to the day info, I suggest looking at the BMW TIS, which you pay a subscription for. I believe a day costs about $20, or you can pay by month, year and so on. The TIS also offers recall info. service bulletins, and repair guides. Real OEM is okay for basic part numbers but if you're going to tackle a repair on your own you might want to check out the TIS.
Sorry, I have the url at work and will post it when I get back to my office tomorrow.
EDIT:
www.bmwtis.com