Well, if you want stuff for underneath, the good old woolly bugger is nearly always at least a decent choice and gives you a good chance at catching a few fish.
But dry flies, rising fish usually happens when there's bugs for the fish to rise for, and the fly should look reasonably similar to whatever they are taking. We just can't tell you what they'll be rising to without knowing more info about when and where. So we're not being stingy, we truly can't make a good recommendation without more info.
What does reasonably similar mean? Afish's list of 1. size, 2. form, and 3. color, in that order, is a great guide. Get the size about right, and you're in the game. Get the size and form right, and you've probably got a pretty good imitation that'll work great most of the time. By form, we mean is it a thick fly, are the wings in the right proportions and in the right places, is it where it needs to be (on the surface, in the surface film, just under the surface, etc.)?? Get size, form, and color right, and well, you have a dang near perfect imitation, the rest is up to you and your presentation skills.