I have paintings and framed prints in all three of mine and have never had a problem with moisture or warping. I'm not crazy about cutesy things in bathrooms (except, of course in kid's), and always appreciate seeing well thought out art in there. In my powder room I have New Mexican art. The kid's bathroom has Western art and our bathroom is tropical Mexican.
I think your bathroom sounds great and a wonderful blank canvas for some art. I'd go with a dark wood frame or frames and nice matting. Try heading over to www.art.com and see what catches your interest . . . just no fish with bubbles, ok ;^P ?

I've never had a problem with water damage to any of our bathroom art either. Surprised me - but the art still looks good after 7 years.

Hi Claire, I have a framed Hmong embroidery and a paper collage mixed media piece in my bathroom. My husband has a giant vintage poster in his. It's not the best idea to hang a work on paper in the paper but if the bathroom shower isn't being run continuously, it's probably not an issue. Of course, the best would be paint on canvas which wouldn't be as subject to humidity. Obviously, if you are hanging a work on paper make sure it is under glass.

Thanks everyone for the suggestions. Nice to know that about print artwork. I always had wallpaper so had nothing else on the walls.

I am looking into Ceramic Tile Art I saw on ebay. These are tiles that are like a painting that you can frame. I thought those would be nice in a bathroom and stand up to anything.
Clare

I'll second what everyone says about framed art faring just fine in a bathroom. A proper framing job probably helps, as does a good ventilation fan. I have some paint-by-number scenes of Vermont I picked up at a flea market a few years back in one of my bathrooms. Cute, kitchy and impervious to steam it seems.