A couple of things to point out (which will probably make things harder for you Jin - sorry!):
SharePoint is always changing. Each new release Microsoft throw stuff out and mash other stuff (including entire separate products) in. They also love to makeover the interface with each new version. They even changed the official SharePoint logo with the latest release! So to base the design on what SharePoint is right now either in look or features, is something that won't stand the test of time.
SharePoint is best thought of as a business platform. It does a stack of varied stuff as you've probably found in your research. This could be anything from public facing web sites (examples), to business intelligence, to search, to collaboration. It's a base to build solutions on top of, rather than a complete solution in itself.
With these things in mind, a design that's fairly generic but tips its head to Microsoft's aesthetics may be worth considering. The overflowing cup logo designed by Sam Dolan and linked to by Kit worked quite well in that regard. (I could only ever get it to look good on a white background however.)
Finally, if there's any chance of us going live with a new design on or by October 3rd, that would fit in really well with the SharePoint event of the year - SharePoint Conference 2011!!