Opera - Glitchy with several "enterprise-class" web applications.
Safari - Webcore sucks as a rendering engine.
IE7 - Quickly coming back as a major browser player thanks to IE7Pro add-on.
Firefox - Top of the game. FF + Ad-Block Plus + NoScript = Security Win. Firebug + Web Developer Tools = Development Win.
Firefox is a solid stable browser for me and the gecko rendering engine is produces pages well (decent font smoothing would be awesome though...).