Canon XTI Lenses?

Depends on what are you using your camera for.

For everyday use, the kit lens is in a very good range. In fact, I'm still using one right now - although I am planning to replace it with the 17-55 f2.8 IS

For portraits, I have the EF 50mm f1.8. It's cheap, but don't let the price left you in doubt - it can produce very good image quality, and I find it very useful in low light condition.

If you're into wildlife photography, I have my eyes on the 70-200 f2.8L IS - to replace my 28-200 f3.5-5.6 USM.

You can get something as Tamron 18-250mm F/3.5-6.3 AF Di-II LED Aspherical (IF) Macro Lens for Canon for $480 or Sigma 18-200mm f/3.5-6.3 DC Lens for $360 but it's better to use double. For example, 28-75mm f2.8 + 75-300F4.5-5.6.

Assuming you already have the kit lens, you'll have to choose between a wide-angle and a telephoto.

Can't help you until you do.