NOTE: 2021 overhaul updates and remarks supersede the original WikiPost. Several details have changed.
DEFUNCT
AuroraFox - Port of Firefox 20 (2021 update: no longer accessible)
Sunrise 2.2.1 - WebKit browser for Web developers (2021 update: last/only version for 10.5 still accessible is an Intel binary only)
NOTE: This is a WikiPost. If you can think of any good browsing clients for PowerPC Macs, please add them.