Try the canon 50mm 1.8. Not exactly a “macro” lens but can certainly be used as one. GREAT depth of field, CHEAP and very fun to play around with. Can take great macro shots and turn around and take beautiful portraits as well.
You can find it online near $100 or less, or in stores usually near $140. You will be hard pressed to find a lens cheaper that does as much as this lens.
T1i is a great camera. I just got mine and have been very happy with the noise level at 800 – 1600.

You may also want to consider third-party alternatives, which comes in at a significantly cheaper price than what Canon has to offer.

Here are a list of lenses that you may want to look at:
- Sigma 105mm f/2.8
- Sigma 70mm f/2.8
- Tokina 100mm f/2.8
- Sigma 150mm f/2.8
- Tamron 90mm f/2.8
- Tamron 180mm f/2.8

Of all these lenses, the Tokina probably offers the best bang for your buck, offering similar levels of performance to the other lenses while still maintaining a (fairly) affordable price. You may also want to get a UV filter for your macro lens, to protect the glass from being scratched (though this is not absolutely neccessary since macro lenses usually have deeply recessed front elements anyways)

I would recommend Canon EF-S 60mm f/2.8 Macro USM Digital SLR Lens for EOS Digital SLR Cameras

Canon 60mm is a great macro lens

or better one Canon 100mm is a great choice.