KeriAnn,
For starting out in macro I would suggest something around 100-105mm.....EF100 or Sigma 105. Most macro lenses are very sharp and there's little to choose between them except build quality and price.
The longer focal length lenses (150 and 180mm) have the advantage of greater working distances for things that get nervous if you get too close. The shorter f/l's (50-60) are generally easier to hand hold.
I have an EF-S60, EF100 and EF180L and all have their specific pro's and con's.
Some other general lenses can produce quite good macro images when used with extension tubes or macro filters. Either of these would be a cheaper option but produce images of inferior quality (most of the time).
Whichever lens you choose, I would factor in the cost of a set of Kenko extension tubes (or Canon's more expensive version of the same). These will increase your flexibility for far less outlay than adding a second macro lens.
Bob