I vote for Camino 1.6.11 that K Shaffer mentions. It is the most recently updated of all Panther-compatible browsers (last update about a year ago). Others are pretty dated by comparison. I find Camino "leaner" and more Mac-like than the others.
x3 for camino. runs light on the system & has built in support for turning off flash, which is a must on older machines. it gives you a play button where the flash would be so you can turn it on when you want it pretty easy.