Perhaps a better question is when and where to take them. Some schools are easier than others and even the time that you take them at the same school makes it easier to "perform" well. ie. My friend in a 7 yr bs/md program took her premeds during the summer to assure her automatic acceptance to the md program.
I tend to do better in classes that I'm really interested in. Even if they're considered harder. I just pay better attention and retain things better.
So instead of taking classes merely to pad my science gpa (which definitely needed a boost) I took physio and immunology and I think came out looking very dedicated. That and I'll have already seen some stuff in med school!
i'm not sure if it will do you any good to take the gen-ed versions of science classes (i.e. CHM 101) that liberal arts majors take (and as far as pre-med reqs go, you have to take the same sh.t that they do anyway--perhaps i just didn't understand this strategy).
anyhow, i would recommend pretty much any 200-level classs in geology, ecology, or other dept's like environmental health etc.
edit: also, in the interest of taking "easy" classes, make sure you don't sign up for a course with time-consuming crap like labs or a term-project.
i actually think upper level science classes taught in a seminar style are good for getting higher grades.
the professors aren't out to get you, so unless you truly screw up, you're going to get a good grade.
plus, your prof will get to know you and will be able to write you a good letter of recommendation.