As I have said before, I think that sex toys can be a great, healthy way to add spice and enhance a relationship. Congratulations to you and your husband for being so willing to try this out.
You do raise a good point though. With so many kinds of sex toys available, how do you know what kind to buy?
You say that you are looking for a dildo, but when some people say dildo what they really mean is vibrator. A dildo is a cylindrical object that may or may not vibrate and is generally meant to be inserted to simulate intercourse. Many women find that using a vibrator on their clitoris is actually more pleasurable, so you might want to experiment with that too.
Generally, you want to start small both in size and intensity no matter what kind you buy. You can always "upgrade" later. Some women find direct stimulation by a vibrator (or a vibrating dildo) directly on their clitoris too intense. In these cases, you might want to try more placing it on a more indirect location, or even using it through a towel.
Ultimately though, every woman (and couple) finds something else to be their favorite. My best suggestion is to browse through MyPleasure.com (or our catalog) as it offers pictures and descriptions of the different kinds, plus we have an interactive Vibe Selector that will really help narrow your choices down. You can even get your husband to help you choose. Who knows -- he might find something for himself too!