I can help to make a side to side comparison between these two cameras. Compared to the T1i, this is how the 40D looks like.
Pro:
- More reliable and rigid alloy body
- Faster and more reliable focusing
- Faster frame rate (6.5FPS vs. 3.5FPS)
- More battery life (1,100 frames)
- Better ergonomics
- Faster controls
- Brighter and larger view finder
- Prosumer camera that feels good
Con:
- Bigger and heavier than Rebels
- Does not have video
- Lower resolution (10MP vs. 15MP)
- Does not have some of the new features (such as Peripheral Illumination Correction)
- 2 years older (07 vs. 09)
The T1i feels like a 50D packed into a Rebel's body and made slow, while the 40D feels like a 50D at 10MP resolution - for the same price, I will pick up the 40D since I think what 40D has is more important than what T1i can offer. Plus, though 2 years older, the 40D may still hold more value when eventually you're looking for selling it.