I think we'd all need a little more info before we could make any suggestions for you. Will this be your first toy? Is there a particular kind of vibrator you're looking for (clitoral, rabbit, internal). Price range?

I'm going to guess you're looking for a first purchase, or you'd know what to ask. Your first vibe should be something simple and inexpensive, that's versatile enough to use internally or externally, and that's made of a safe material. Whether you get something small or medium size depends on your sexual experience. Don't get anything huge regardless, not for a first toy.

I'd suggest something plastic, like the Doc Johnson Velvet Touch, or maybe something silicone, like something from [this|link] line, which just happens to be on sale right now.