One option is the 20-35 USM. I know it will focus close enough to fill the frame with a 6" subject, and it will give you a moderate wide-angle to longish-normal range. With that range, you'll be able to emphasize the shape of the object dramatically (using wide-angle perspective) but still make images of normal perspective on the long end. I have personally tested this lens in closeup details (see the photo I took of the name plate on the Big Dog motorcycle in my thread in the shared photos folder), and it seems as sharp as the 10D's sensor. Of course, the 10D only uses the sweet center of the field.
Another option if you want less drama but the ability to shoot fine details is the 50mm macro. This will give you a short telephoto lens on the 10D, but one with the ability to focus on a patch of wood grain as little as two inches wide. It's not too long to use as a general-purpose lens, but the 20-35 is probably more useful there.
The 50 is sharper and constrastier than the short zoom, of course, but it won't matter much unless you will be making prints larger than 8x10. Both will give you all you could hope to have in web-page and brochure photos or for a portfolio of 8x10's. If you have money left over, spend it on lighting equipment, which will give your images more drama than any lens.
Of course, there are many lenses in the normal range that might do as well as these, but I own these and know myself that they would do what you describe. Others will fill in my blanks, I'm sure.
Rick "who loves images of wood grain" Denney