AndyA - 2:47 pm on May 22, 2012 (gmt 0)
I've never had large numbers of old product pages to remove as in the OP, but what seems to work well for me is to just change the robots meta tag on the pages to "no index, no follow."
There have been a couple of times when a product was later updated, improved, or a new product was released. I was then able to update the old page, change the robots meta to "index, follow" and the page returned to the SERPs in a few weeks.
I've always felt that Google in particular doesn't like it when a page suddenly disappears. It either wants to be redirected to a new location, or at least find the old page, even if there's nothing on it. I usually strip down the old pages to remove most of the old content from them, and make sure I'm not linking to them from someplace else on my site. I also add a "Sorry, this page is no longer being maintained, please see..." message to the page to catch anyone who somehow manages to find it, perhaps by using an old link from an external site.
I value netmeg and g1smd's advice very much, so their suggestions might be best, but this has worked well for me over the years, and it's another option to consider.