Many parents equate getting an ultrasound with finding out the sex of their baby. Of course, from a medical perspective, that isn't too important, but it may mean a lot to you.
Knowing the sex can cut down on the time spent debating over names, but really it is only one piece of information: you still won't know who the baby will look like, or when he will sleep through the night. Some parents-to-be who are going to be really disappointed with one sex or the other tell me that they want to find out ahead of time so they can adjust. Others like not knowing-since this may be the only time that you get to "have" the gender baby that you want-at least in your fantasies.
Sometimes sex can't be determined on ultrasound-the baby may be positioned in a way that hides the genitals from view. Unfortunately, since finding out the sex doesn't qualify as a medical reason to have another scan, your insurance probably won't pay for it; unless another medical indication for ultrasound pops up, you may have to live with not knowing until you find out the old-fashioned way-at birth.