Non-L primes: add ring USM, faster aperture, better IQ, more apreture blades, and IS where applicable - 20mm f/2 USM, 24mm f/2 USM, 35mm f/2 USM, 50mm f/1.4 [IS would be nice for APS-C cameras], 85mm f/1.8 IS USM, 135mm f/1.8 IS USM.
A new lens to compete with the Nikkor 14-24mm f/2.8
A big, healthy, resounding upgrade to my wallet, so I could buy all of the above, as well as the 8-15mm f/4 L, TS-E 17mm f/4 L, and 200mm f/2 L IS USM.