No pics but it's a great place to put plants, pictures even display art.

Do you need space for books? As long as you use bookends it might be a good spot for those.

I've heard of people making shallow trays and adding pebbles and water and setting potted plants on them. That might be a good way to add some humidity to the house, too.

I think you should decorate them as if they were any other small table top.

I'm with kwsl and agree that attempts to decorate them look cutesy.

If you are compelled to add something, I'd do trays of plants in water.

The heat will dry out and ruin many items, as I'm sure you know.

I'm in the camp of not every surface needs to be adorned.

If you do want to decorate them, I would look for pieces that stand well on their own, an interesting oblong container, a wonderful tray, etc....
things that have a texture or color that make them look unique on their own,
not a staged vignette of assorted items. A pile of books could look good also.

I also agree that they don't need to be decorated ... and do you not live in an area where you turn the heat on?

Anything on top of the register would get ruined.

How about just a decorative radiator cover?

pamghatten, they are covered.

Thanks all, for your replies and good ideas!

I do especially like the idea of plants, and we could certainly use the moisture they would provide. Thanks again!!

...Robin

We have a ton of radiators with wooden covers, so I understand wanting to do something with them. In our sunroom, I have plants on one of them. They are not affected by the heat even though these radiators have metal covers, so the tops are warmer than the ones with the wood covers. My kids use them as nightstands, basically, since they are next to their beds. I have a collection of "artsy" glass hearts displayed on the dining room radiator cover. I have seen quite a few of my neighbors display family photos on theirs. That, to me, might fit in the too-cutesey category.