What do you think is the best memory card for a Canon eos rebel t1i camera?

Hello and thanks for your question!

A Canon T1i! Total sweetness (even if I am a Nikon fan)! For the power that the Canon T1i delivers you'll want a memory card that writes fast enough for the amount of pictures you'll be taking especially if you're like many and you like to keep hitting the button trying to get every picture possible. Shooting at 3.4fps you don't want a card that will leave you hanging at any point. So your best bet are SDHC cards. 

SDHC cards are a higher class of cards than SD. They write faster than their first generation brethren and are becoming the standard for devices all over today. The only sad part about it is that to get quality product you have to spend quality money. 

At 15.1MP per shot (I'm sure you could decrease this from the standard but that also decreases photo quality depending on the shot especially) you'll need nothing but space. 8GB is the utter minimum that you'll want for a casual shooting expeditions if you're trigger happy. I included an SDHC Class 2 here because it is cheaper and though it writes slower it can moderately keep up with casual expectations. 

I recommend the 16GB Adata card because it delivers a Class 10 shooting experience and has enough space that you can forget for a while about changing your card out. The site is also offering free shipping on the product so you end up saving compared to the other 16GB card that I would have recommended provided that this one had not come along, lol. 

I wish you happy shooting!