Radiators can take up quite a bit of space in a small apartment. But do you know what helps? Resting a shelf on top. Make sure you aren't storing books or flammable objects there, but think of it as a warming side table where you can perch a cup of joe when you're curled up on the sofa! Here are a few examples:
In the warmer months, of course, the shelf can be used in any way you please. Then, when winter comes around and those babies start heating up, clear them off and use them only as appropriate for a hot surface.
We recommend a stone slab, as shown in all of the examples above. It's more durable than wood, which could warp and crack over seasons of extreme temperature swings. Marble saddles from the hardware store can work remarkably well for this application: they come in a suitable size (around 36" x 5") and they're pretty inexpensive. Of course, other solid materials like Corian could work, too.