What plant should I use for my science experiment?

Just a flower, the effects on them are easist to recognize.

what ever you want

I think a good plant to use in this situation would be to use a Vines Fly Trap.

I'd recommend beans - common old garden white or red beans you can buy at the grocery store (or alfalfa seeds - buy them at a health food store). They sprout and grow quickly, and are better than grass (which would also be a good choice for most plant experiments) for this experiment because they have broad leaves which can display the effects of the pharmaceuticals better. It is best to plant at least 15 to 20 seeds per treatment group, since just a couple won't be a large enough number to show variation and get statistically significant results. Be sure to rotate their positions during the experiment, to eliminate this as a potential variable: even if it appears that they are all getting the same amount of light and air currents, they might not be - and besides, these are the little things that teachers love to see in this kind of experiment - the more attention to detail, the better!!