- Uzbl: http://uzbl.org/ Haven't had much luck with this one, but it's quite interesting. A while back, there was some work into getting this to play nice with emacs (google: Ezbl)
At one point I used and loved Vimperator and then migrated to Pentadactyl, but ultimately got fed up with Firefox's bloat and memory management issues.
I'd recommend checking out Firefox Aurora (http://www.mozilla.org/en-US/firefox/aurora/) - Firefox is really looking great these day. The new native developer tools are coming along nicely and hopefully will prove more stable than Firebug.
There's an Arch Linux dev that maintains a custom repo with Aurora builds and matching Aurora Pentadactyl packages in the AUR, for those on the distro.
- Luakit: http://luakit.org/projects/luakit/ My favourite in this list. Just webkit + lightweight lua shell. Infinitely customizable.
- Surf: http://surf.suckless.org/ From the same people who created wmii and dwm
- Uzbl: http://uzbl.org/ Haven't had much luck with this one, but it's quite interesting. A while back, there was some work into getting this to play nice with emacs (google: Ezbl)