On a Mac, I really like Camino for it’s sleekness and speed. It’s built around the same engine as Safari, yet still seems quite a bit faster to me.
I have to mention though, that I like my browsers “au naturel”. I keep plug-ins and extensions to a minimum.
When I do actual research, I use Devon Agent.
I used to really like Firefox back in the 2.2 days, have to say though that it seems to me it is becoming an add-on delivery machine, so it doesn’t appeal to me that much anymore.