The A710IS ranks high on my list. My wife uses one, and it's perfect for her. I recentlybought a used one in good shape for $25, and then found an A720IS in very good condition for $45 that lives in my car.
I really liked the S70. I did try the S80, but didn't like the location for the mode dial. Images were no better than the S70.
I used an S90 for four years, and just recently "up-graded" to an S95; which is fractionally better.
Other standout Powershots were the SD850IS and SD870IS, and the very nice SD950IS with the sensor and processor from the G9 and a voluptuous titanium shell.
Then there was the S3IS and S5IS. Really nice cameras, except for strong chromatic aberrations in high contrast situations. Sharp and fast lenses, minimal noise reduction, and crisp looking images.
Two more stood out for me. The remarkably sharp G5. It was noisy at ISO 400; but had an excellent f/2-f/3 lens, and really good dynamic range. I liked the G7 a lot; but it had a badly designed optical finder, so it took some learning time to use it well. The G9 was very similar; but added a 12 MP sensor, RAW, and a 3" LCD. Overall, I preferred the G7.
Finally, there's the Canon Pro 1. A great lens, an 8 MP, 2/3" sensor, great color, and terrific image quality - provided you had a later production model, as it was a work in progress with several improvements over it's lifetime. It had its faults, make no mistake, but in the right situation it was excellent.