First of all I confess that for me, Canon has the best image quality Ive experienced. A520 and A620 make no exception at all. The Canon A520 is just slightly smaller and definitely lighter than the A85 it replaces (A520 only uses 2 AA accumulators, however, A620 comes back to 4 AA which last longer), but still hardly fits in your bag (sort of robust compact design).
They can be used as a point-and-shoot camera in Auto or Program mode, but it’s special ability lies in the flexible exposure control it allows: Shutter-Priority, Aperture-Priority, full Manual, and easy to use scene (Kids&Pets, Fireworks, Beach, Foliage, Snow, Underwater, Indoor, Night Snapshot) and modes (fast movement, slow movement, portrait, night, landscape and, particularly for canon, panoramic mode).
Also, you can choose evaluative, center-weighted, or spot metering, vivid colour, black&white or sepia. Kind of slow cameras when flash is used. MMC (Multimedia Memory Card) for storage.
As for the technical details, A520 (released in February 2005) has a 4x optical zoom, 4 MP, F2.6 maximum aperture, 15-1/2,000 sec. shutter speed range, 35-140mm (35mm equivalent) f/2.6-5.5 zoom lens, powerful noise reduction and minimum ISO 50 (not 80 as other cameras), at superfine resolution you come up to 180 instead of 75 pixels/inch, 1.8-inch LCD. But movie clips can be recorded only of up to 3 minutes, with sound.
A620 is different than A520 by its 7.1 MP and the 2.0 inch LCD that flips out and rotates.
Since I mentioned A520, theres also to take under consideration A530 (5 MP) and A540 (6MP), but, to conclude, A620 is the last and the best from this series, therefore, my recommendation.
Optional accessories: wide-angle, telephoto and close-up lenses, an external High-Power Flash, and an underwater marine case for underwater photography.