This has gotten around the Internet pretty well, but just so there's no excuse for anyone not to have seen it: Kate Beaton's series of Lois Lane comic strips does a really good job of showing how cool that character should be. There are only two explanations for Lois' never figuring out that Superman was Clark: a) she was too dumb to put it together; b) she was too busy to care. I know which option DC continuity endorses, but I also know which one I prefer.
Beaton admits to not having read a lot of Lois Lane comics, but that's probably for the best. Her interpretation is based instead on Lois and Clark, old Fleischer cartoons, and Dean Trippe's unpublished Lois Lane, Girl Reporter pitch.