Depends on how much you want to spend Rob.
You can get the CANON 180mm f/3.5L Macro but that's around $1600
Very sharp but a bit slow in AF for terrestrial, still a top choice IMO.
Or there's the CANON 100mm f/2.8 Macro for around $600.
It's a great macro lens, very popular.
Also good for astro work.
Then there's the wider CANON 50mm f/2.5 Compact Macro Lens for around $300.
Again it's a nice macro, gives a nice fov for wide astro shots.
The newer CANON EF-S 60mm f/2.8 Macro Lens is one I have not had any experience with yet so can't comment but suspect it would fit the bill nicely.
Only thing is, if you ever upgrade to a FF camera like a 5D then you won't be able to use this lens on it.