I find it incredibly hard to find jeans that fit my (rather muscular) seat and thighs properly without looking too loose and baggy
The only jeans that ever fit me perfectly were from Willis and Geiger, but they're long out of business.
For khakis, I really, *really* like Bill's Khakis, but I still have to buy 'em one waist size too large (to get that seat/thigh room) and then have the waist taken in.