Internet : IE9 at work, 'cause everything just works no hassles or hangups. Intranet pages are all sharepoint, which just never seems to work 100% if not on IE. Firefox for general browsing at home, purely because of the high level of customisation it provides. I also have Chrome, Safari and Opera installed just for good measure. Rarely use them, but have come in handy if another browser fails for any reason.
Email : Outlook 2010 at work, also get my mails on BB via BES. At home Thunderbird, because it works without giving any hassles.
Anti Virus : BitDefender 2010. Relatively low overhead to run, regular updates, easy to use and it has Game Mode.