I'm getting used to how Plot works, and I have to say that the learning curve is there but not too steep. So far, I've been able to put together some nice plots with per-data-point error bars from copy-paste and from file import without too much hassle. Playing with things like line-widths and point shapes is a breeze. And, at least for my simple needs, figure quality leaves nothing to be desired.

Produces very sophisticated plots. Bit of a learning curve, though.

After trying the mess that is gnuplot on OS X, I was very happy to find this program, which makes beautiful vector plot. I have found it to be much more powerful than gnuplot, and it also has a nice interface.