Not to hijack Angus' very worthy thread, but…
...I'm a two-lens guy, so my suggestion, for anyone who needs to pack small-ish, is a Nikkor 90mm f8 and a Fujinon 210 f5.6 (older, single-coated version).
They're both 67mm filters, combined weight is about 800g, and both give tons of movements on 4x5 (the 210 can easily serve as an 8x10 lens in a pinch).
Armed with a 90 and a 210, there's not much you can't do on 4x5.