Being on a trip with a car in Australia or New Zealand, I dont mind carrying along heavy lenses like the Canon L 100-400, whatever I dont use I can keep in the boot. But sometimes on walk-abouts I prefer to carry less. I decided to go for 2 more prime lenses. The 50/1.4 and the 100/2, despite not being L lenses they are lightweight, very sharp and worth the "little" (as compared to L lenses) money. Both match very nice with the 5D II.
I can recommend Ken Rockwells reviews: