My kit contains 65, 90, 135, 150, 180, 240 & 350 lenses. That being said, my favorite is the tiny and outrageously sharp 135mm 5.6 Apo-Sironar, wow, what a lens with nice coverage!
The 90 6.8 is fab as a wide and sees a lot more use than my rarely used but still useful 65 Grandagon. The 150, 180 and 350 Schnieder Apo's all use 58mm filters so that is nice.
And then of course is the fantastic little Fuji 240 F/9 A.
I find that unlike 35mm or even 120, I need more lenses in the field with the 4x5 because it is 100% tripod mounted, so I usually opt for all of them on road trips and 5 of them when hiking.
But seriously, pick up a clean used 135 Apo-Sironar and you are set, brilliant lens!