Last weekend we refinished our house's original vestibule door. While Patrick was sanding off the layers of old paint and adding a few new coats we repainted the hardware and replaced the knobs with some crackled porcelain knobs that I found the weekend before.
Hardware is one of my favorite things to DIY - replacing old drawer pulls with vintage ones or even just adding a fresh coat of paint can completely change a space.
Luckily for me, my door was already fitted with vintage hardware, so it was easy to replace the knob - my door's spindle (the long metal piece where the knobs are attached on either end) is much smaller than any other doorknob sets I've seen, but I was able to simply unscrew the knobs and screw on the porcelain ones - leaving all of the actual hardware and internal mechanisms intact.
I highly recommend unscrewing all of your door hardware, putting it into a ziploc bag, and bringing it and a few screwdrivers with you when you go hunting for new knobs - that you'll be able to make sure that your new knobs and spindle will fit into your latch. I visited Provenance Architecturals and ReStore in Philadelphia - the owners at both spots were more than happy to help me make sure that my new doorknobs worked with my old hardware!
Check out DesignSponge's "Best of Hardware" for more inspiration! Which on is your favorite?