My lo is into anything and everything at the moment as he's crawling so everything is new and interesting to him.
I'd say go for something that they can't break bits off and eat. It also can depend on what gender they are. My son loves cars and garages, where as i don't think that would interest a girl so much.
Maybe a toy phone would be good, Oliver's constantly grabbing our mobiles or phone, so he's got a toy one to play with, it has to flash though because he knew that a plain one wasn't real.