Try connecting the camera directly to the Mac and using Image Capture, but I suspect that since the camera isn't happy with the card (and cannot read it) that won't work either. The only reason I'm suggesting it is so that you know you've tried all possibilities! You would need to be able to get the pictures OFF the card using Image Capture - it won't mount the card on the Mac's desktop that way, so connecting the camera to the Mac won't allow you to use recovery software.
If you cannot get the card to show up via your card reader, you cannot use recovery software - as you've already figured out.
I would second Jim's suggestion to try taking it to a camera shop (one geared towards the pro crowd, not a place that just happens to sell cameras along with all sorts of other electronic gear) - mostly in the hopes that some other flash card reader will actually work.
Beyond that, your only choice is a data recovery outfit and as we all know, that's incredibly expensive usually.
One other bit of software I'd try (actually, I'd try it first) is
http://www.datarescue.com/photorescue/ - made by the same folks who make DataRescue. They do mention even being able to get something off a card that isn't showing up as a drive letter (on a PC) but is still electrically responsive. I'm not sure that your card falls into that category, but worth a shot.
Also - have you checked the card carefully to make sure there is no grunge in the little holes on the card where the pins go and also checked that there are no bent pins anywhere, though the likelihood of bent pins on both camera AND reader are slim, unless there is something blocking one of them?
