At least the question Kai and the staff at DigitalRev are trying to answer. They took a Canon 100mm f/2.8L Macro vs the Canon 100mm f/2.8 Macro approach. So, if you want to know what’s so special about L lenses, then this is the right video to watch.
Be aware that there is an August Lens Rebates program going on. You can get the mentioned lenses with some consistent discount. Check the EF 100mm f/2.8L Macro at Adorama (refurbished here) and B&H, the EF 100mm f/2.8 Macro at Adorama and B&H.
EF 100mm f/2.8 Macro price check: Amazon, B&H, Adorama, Canon USA, J&R, Digitalrev, eBay, rent it at Borrow Lenses
EF 100mm f/2.8L Macro price check: Amazon, B&H, Adorama, Canon USA, J&R, Digitalrev, eBay, rent it at Borrow Lenses