Have you tried painting them to match your walls?

if your talking about the floor registers, lowes has some decorative vent covers for reasonable prices.

Have you seen this?

Dayna

Here is a link that might be useful: DIY Return Air Grilles

They sell these at Home Depot...

Here is a link that might be useful: Decor Grates

I have a several Reggio Register covers (cast aluminum) that I love. Most of the ones I have are air returns, but have a couple of floor registers as welll. They sell the adjustable louvers separately. The bad part is they are pricey. At it took me 10 years to bite the bullet and buy some for the main living areas. As hefty as they are, they will definitely outlast the life of the house.

Here is a link that might be useful: Reggio Registers

Have the ones form HD and they are a bit flimsy. If you have HW floors, they also have wood registers. Mine look like new after 5 years.