It'll appear on ebay again, so don't worry. Thought I'd chime in here. I've heard the Rattle second, but, although I'm in a minority here, prefered the Klemperer. Still, what has been said about Rattle's version has piqued my interest. I do promise not to bid at ebay for a 60 day period though, so as not to upset the line order here.
I currently own five Mahlers, but the one that I find myself listening to most often, just cause it's so purdy, is his Symphony No. 4 with Szell conducting. Not only is it beautifully paced and warm, but Judith Raskin is impeccable as the soprano. I know this is simple in terms of the usual complexity of Mahler, but it's so beautiful, it would be a shame for any Mahler or classical fan to miss imo.
If anyone is interested it's available on Sony Essential Classics. Nice recording quality too.