Welcome to the board. Sorry to hear about your friend, it's always sad to lose a friend particuarly a Wildhearts fanatic. The Wildhearts are one of those rare original bands that just hook you and never let go and make ordinary souls into obsessive fans for life.
As reverend Shiney said,
Earth Vs. The Wildhearts (1993) is your best place to start. Just 12 songs of sugary poptastic hooks dressed in all manner of shabby heavy metal and punk clothing.
P.H.U.Q. (1995) is the next one to get, again brilliant. Hookier even then the debut and provides sleepless nights for me when deciding their best out of this and the debut.
Then after that it could really go either way. Their new one
The Wildhearts (2007) is brilliant and so is
The Wildhearts Must Be Destroyed (2003) or
Riff After Riff (2002) which is exactly what it says on the tin.
But don't take my word for it, check the link Eyesore provided. There was alot Wildhearts jabbering going on in there so you can get a feel for what other people think about this bands essential rock n' roll catalogue.
Anyway run along now, you've got some shopping to do.