When my older kids (now 10 and 11) were little (and now with my 3 year old), they go sit on Santa's lap at the mall because it's too cute to pass up, and they tell Santa what they want for Christmas to help give mommy and daddy some ideas of what they might want. Then mommy and daddy (and grandma and whoever else) get them gifts. Christmas morning, they open presents and we let them know who each present is from. Period. Santa is a nice guy-- we give him hugs and take a photo with him-- just like Chuck E Cheese and Mickey Mouse and the Cow at ChickfilA!! We don't tell any stories about him coming to our house and giving our kids presents. When they watch cartoons about Santa, they are fun fiction just like when they watch Disney movies and other cartoons and we don't relate it to "real life". Let your close relatives and friends know that you will not be doing Santa and even if they think you are crazy they will hopefully respect that and not say anything to your child. If they do say something in front of your child, watch to see if she heard-- you can just let it slide, or you can say (while she is listening) something like they are being silly, that the presents really came from X. As they get older (around kindergarten age) if you decided to stick to it, it's important that you explain to her that different families believe different things. Let her know that some families tell their kids that Santa comes to their house with presents and we don't want to ruin their fun or upset them so don't tell them that we don't do Christmas that way. As she gets a bit older and older, just speak with her in an age appropriate way. Let her know that it is very important to some families that their kids "believe in" Santa and it is not good manners for her to tell them otherwise.
***I just wanted to add this...
One poster said she never knew anyone to be traumatized by finding out the truth about Santa. Well, I know someone. I wouldn't call it traumatized, necessarily... but he is the youngest of 6 kids. When he found out the truth about Santa, all of his siblings had already known for years. He swears he was less upset about Santa and more upset that his entire family had "tricked" him and/or "lied to him". I think that's silly, but he really was very upset and remembers today how upset he was as a child. He swears that he had a hard time trusting anything his parents and siblings said for a very long time. He started questioning everything, including his family's strong Christian faith (because he wasn't sure if everyone had been lying to him about God, because after all he never "saw" him just like he never "saw" Santa)