Most of the ones I listen to have been mentioned already.

Little Atoms - an unashamedly smart podcast about just about everything discussed from a scientific/sceptical point of view

And of course large chunks of BBC Radio 4 is available in podcast form, though I'm not sure whether they are available to you colonials ?

I also listen to a bunch of coding podcasts on and off. Including Hanselminutes, .NET Rocks and sadly not Stackoverflow anymore