20D over 350D/XT:
1. 5 vs. 3 fps
2. 9 pt AF with high-accuracy center cross sensor when used with F2.8 or faster lenses vs. 7 pt AF and no high-accuracy sensor
3. 6 frame RAW vs 5 (or 4 when shooting RAW + JPEG)
4. 21-23 (depending on spec you read) JPEG buffering vs 14
5. 1/8000s max shutter vs 1/4000s
6. 1/250s flash synch vs. 1/200s
7. 8.2 Mpixel sensor vs. 8.0 (with some other differences probably due to modifying sensor for cost and elimination of circuits needed for higher frame rate readout)
8. ISO 3200 max vs ISO 1600
9. Magnesium body vs. polycarbonate (with steel subframe?)
10. 118,000 pixel LCD vs. 115,000
11. Slightly higher viewfinder mag
12. More custom functions
13. Larger capacity BP-511a battery vs. NB-2LH (half the capacity)
14. Command dial and joystick on back vs. compass-button pad
15. Secondary LCD on top vs. back
16. No auto-pop-up flash vs. auto pop-up
17. Selectable embedded JPEG with RAW vs. one fixed siz