MikeDog mentioned the jack rabbit--I doubt you could wrong with one of those. It's the most popular type of vibe on the market. This is a plug, but a well-intended one, I assure you, the

store has the jack rabbit at a very good price at the moment. (Just click the link in my sig, then the link for the toy store on the left-hand side. If you look at the "best sellers" list on the right, you'll see that the Jack Rabbit is no. 1.)
Other than that, I can't think of anything specific, just things to look for. If you want something long-lasting and easy to clean, silicone is the best material for sex toys. Fun Factory has some awesome vibes (carried by various etailers), but some of them are pretty thick towards the end, just a caveat.