EF 14-18mm/2.0 L IS USM - if too heavy and awkward, then 18/1.4 (below) may complement the line-up better
EF 20-35mm/2.0 L IS USM
EF 40-85mm/2.0 L IS USM
EF 18mm/1.4 L USM tweaked for astrophotography, minimum focus distance about 24cm, if possible 17mm/1.4
EF 17/2.0 L USM with slight (50%) fish-eye-characteristics intended for underwater-photography and close-ups
EF 15-30/4.0 L USM FF-Fisheye
EF 18-70/4.0 L IS USM (complementing the 70-200/4.0 L IS USM, eliminating need for extra wideangle in the bag)
EF 35-100/4.0 L IS USM Macro (complementing the 16-35/4.0 L IS USM and 100-400 L IS USM)
EF 35-100/2.8 L IS USM Portrait/Macro (complementing the 16-35/4.0 L IS USM and 100-400 L IS USM)
TS-E 20-30mm/4.0 (IS)
TS-E 35-60mm/4.5 (IS)
TS-E 65-120mm/5.6 (IS)
EF 38mm/1.2 L IS
EF 66mm/1.2 L IS Macro/Portrait
EF 300/4.0 L IS USM II excellent
EF 360/5.6 (L) IS USM affordable, lightweight, plastic, yet near L-quality optics
EF 200-500/5.6 L IS affordable
EF 500/5.6 L IS USM excellent
EF 800mm/8.0 L IS USM excellent