The oldest digital camera I have that I still use (and I use it quite a bit) is a Canon A630. I sort of hate to say it but this camera has given me the least grief of any digital camrea that I've owned, and has also fulfilled my expectations better than any DSLR I've had, especially when I consider what I paid for it in early 2007. If it had IS and shot RAW natively rather than with the (kludgy but interesting) FW "hack", it would still be worth buying today, IMO (thoguh a higher-res screen would be nice!)
The "dumbing-down" of the Canon A-series makes me sad! The 4-AA models were much snappier in operation than the 2-cell ones, putting the batteries in the grip gave them a really nice balance, and battery life was improved out of sight. I guess the last of the line, the A650IS, was a bit too close to a G-series in terms of specs, though I never thought the image quality from that particular 12MP chip was as nice as the 8 or 10MP ones (my Dad has one so I've had plenty of time to fool around with it to compare it to the A630)
Scott