This is a legit question what with Panther just out.
Yes, Opera does make a Mac version, but it currently sucks. I use it for compatibility testing, but that's just about it.
If you're not a Safari fan, I'd say you've pretty much got Firebird, Camino, and OmniWeb to choose between.
OmniWeb has a cool interface, and it uses the same renderer as Safari--that can be a problem or a benefit, depending on the sites you surf. It's not free, though.
I still use Camino, but I admit that version 0.7 (the current stable version) has a few rendering glitches, and the current nightlies are no help. It's good enough for me to stick with at this point, but if they don't get the rendering bugs worked out in a couple months, I'll probably start seriously checking out Safari or Firebird. My wife has already gone to Safari, since the glitches are more severe on Japanese sites.
Firebird is actually looking really good. It uses a slightly newer version the gecko renderer that Camino uses, but in any case the glitches are not there--best rendering of any browser on any platform at this point, if you ask me. It doesn't look very good unless you add the Pinstripe theme (practically a requirement), but with it it's pretty good, and has a lot more preferences than Camino. Not as elegant, but still acceptable.
Mozilla is also an option, but it's just too bloated (and the Pinstripe theme hasn't been updated for the newest version) so at this point Firebird is really looking like a better choice all around. it's also the direction the Mozilla project seems to be headed overall.
iCab is plugging along as always, but unless you've got a VERY slow computer, it's mostly just good for quick HTML-validation checks.