What do you have for lens(es) now? That could affect your choices. If, for example, you already have an 18-55 kit lens, there's no need for a zoom with a similar wide end. If you have just a nifty 50, then you'll want a zoom with a decent range, say 28-135 or my personal favorite (I used to have one), 18-135. That way you'll have a reasonable wide angle and a nice telephoto range all in one.
Although I'm not "into" macro photography (yet), I did experiment see what the 18-135 could do with flowers. Hand held, I simply looked at what the closest focusing distance was marked on the lens (about 2 feet), picked a flower and zoomed in. Very respectable results. I'm sure I could have zoomed in on an ant or two and gotten satisfactory results, too.