The 100mm Macro is a beautiful lens. If you can afford the VR version I would go for it. However if you want to try out Macro on a budget, if you have a 50mm lens, just buy a reversing ring. Not too good in the edges but certainly good enough to play around with. Cheers, RI
For the relatively small difference in cost (compared to other non-L / L series differences), the L series version is well worth considering as the stabiliser is a godsend for spontaneous shooting. Without the stabiliser you'll need a tripod and/or flash.
It's probably worth mentioning as well that Canon have superceded the MR-14EX macro ring flash with a mk2.
The old one is still available at ~£150 cheaper than the new one and it supports IR wireless TTL wheras the new one is radio wireless to work with the likes of the new 600EX speedlites, so this may be of importance if you have some older Canon units with IR TTL while the old MR-14 is still available.
I shoot macro but had to go for the 180mm as all the shorter length lens brought me too close to the reptiles especially within the strike distance of adders. http://www.skid2me.co.uk/skid/family/pages/112add.htm
I see that the ring flash MR14 EXII has still not arrived but is on back order from WEX and Calumet.
I've got the non-L 100mm and it must be said it makes a belter of a portrait lens, the only thing against it is the AF is a bit slow and tends to hunt around (as it probably does on all genuine macro lenses). Optically I don't think there's much between the L and non L (personal observations, although it could be mine is a good one when comparing against the L one I've used)