You probably can't go wrong either way. The L has IS which can help with hand-held shots. I've only used the L version and it is a brilliant lens and I like that it is very light as well (plastic versus metal but it does not feel cheap at all). I think the collar is optional - and very handy - should be included. This is the kind of lens you wish every lens you have would be like; reasonably fast, light, solidly built, smooth operation, and brilliant images.
The 500D is handy to put in your pocket if you are just walking around with a general lens and want to be able to get close if you need to. I have used it a handful of times - probably would not buy it again after having the 100/2.8 macro. Extension tubes are another inexpensive way to get closer with existing lenses and they have no optical effect - worth looking into as well.
I agree that the 100mm f2.8 macro lens will give much better images. Optically I don't think you can tell the difference between the f2.8 and the f2.8L. The extra cost buys IS. If you will be shooting hand held it is probably worth it. However, shooting macro hand held is very difficult even with IS. The IS will help with camera shake but not with loss of focus. With macro you are usually dealing with very shallow DOF and it is very difficult to keep from moving the camera forward and back slightly. Using AI Servo mode will help with this. I own the the non-L 100mm f2.8 and shoot on a tripod or using flash so I have not missed the IS.
Canon T3I camera, EFS 18-55mm lens, EF 75-300 zoom lens, and a EFS 60mm ultrasonic macro, also I am new at photography and I have fallen In love with It, taken some nice pictures at least that Is what my friends tell me. I am studying Scott Kelby book volume 1. Just turning 60 years old getting ready to retire and I need a safe hobby. I Am Into outdoors photos, bugs, flowers, wildlife, waterfalls, spiders,snakes, even rocks and thanks for helping me out. What about a wide-angle lens.