Well... as I have been using a 7D, I'll list my ideal 5 for that (I think APS-C vs FF body HAS to be stipulated, otherwise lens choice doesn't sit within 100% context!)
1) Sigma 8-16mm - must have great, sharp, contrasty IQ & an accurate AF copy too.
(I have a good, sharp copy of the Sigma 10-20mm, which has minor AF issues - but it's not a practical problem how I use it)
2) Canon 15-85mm - I have this lens, love it as my walk around... great range, v good IQ all round
3) Canon 100mm L IS USM macro
(I have the Canon 100mm non-L USM macro, which for all intents and purposes is 99% as good for macro.. but does lack the weather sealing and Hybrid IS- mostly for handhelds non 1:1 shots)
4) the yet to be released (maybe not even designed... CR2?) Canon 50mm f/1.4mm USM IS
(I had two copies of the 50mm f/1.8, didn't like it's AF nor bokeh, and not quite good enough IQ wide open). There are aspects of the current Canon 50mm f/1.4 and Canon 50mm f/1.2 L that I don't like....
5) Canon 200-400mm 1.4x L (for my love of wildlife, especially birds - yes BIF too)
(I have the 70-300mm L - terrific IQ at any setting- and if I got the 200-400mm 1.4x would desparately miss the portability of the awesome 70-300mm L... so it would be a 'toss up', but one can't argue with a lens that has 200-560mm range in an L!)
Yes, I'd probably like a 200mm f/2 IS, or a 17mm T/S lens as an 'extra' - but the above 5 lenses are what I would expect to use lots (as I do all my current lenses). So I feel that with what I currently have, I'm actually not too far off what would be my 'ideal' 5 lenses anyway, actually. And that's a good thing!