sparrow is the best Gmail client. careful, im not sure its for other mail services yet...
i used vitamin-r for a while, i swear it made me more productive. Xee as a photo viewer, cos preview wont do moving between images in a folder.
itsy - lightweight twitter viewer
growl - for the notifications
transmit for ftp
coda for the coder
xcode, cos i need it
vuze/jdownloader for the downloads
ps3 media server for the streaming of the dwnloads
if i migrated to a mac again, i'd be tempted to separate users, ie have a work user and a matt user, to keep my files separate from the business files.
if this gonna be that kind of party im gonna stick my dick in the mashed potato.