Before deciding the camera is faulty, test the cards and camera separately. Try the CF cards in another camera or reader, and try a known-good CF card in your XTi. CF cards can fail, and repeated corruption may be a card issue rather than the camera.

Also format the card in the camera itself after backing up your images, since in-camera formatting is often the most reliable. If a simple in-camera format restores normal use, the camera may be fine. If corruption continues with multiple known-good cards, then the camera may need service.

If the camera is still under warranty, contact Canon first since repair may be covered. If it is not, whether to repair or replace depends mostly on your budget. For a lower budget, a used body can make sense; for a higher budget, a Canon refurbished body is generally a reasonable option. If possible, check condition and shutter count when buying used.