Volvo: squealing brakes, rust buckets, squealing brakes

Question
I remember this problem with my 144 and countless ragged early 240s when I was younger.  In those days I was just glad the cars actually came to a stop with as little money as I managed to put into these rust buckets!  Now with a '93 850 I gained through marriage, I have a little more in the way of resources to solve its various annoyances.  Have tried a variety of pads, shims, caliper grease, etc, but the front brakes on this car continue to squeal at low speed stops.  Any ideas?

Answer
Unfortunetly it sounds like you've tried a lot of what I would have suggested.  One thing that has seemed to work for me in the past is simply to buy the most expensive anti-sqeak pads I could find.  I think in this area, money really makes a difference.  However, one other thought comes to mind.  If your rotors themselves are warped or grooved (i.e. the discs themselves),  then they would cause uneven or grooved wear of whatever pads you had in, and in turn, probably encourage squeaking, especially at low speeds.  Run your hands over the inside and outside wall of each disc on the car and check for circular grooves, or actual disc warpage.  That might be part of the cause.