I recently did a survey on sex toys. The results can be found here (scroll down to SEX TOY SURVEY). What you most need to know is below.
The sex toy most used and most liked by both men and women was the egg or bullet vibrator. Over half the couples in our survey had tried this kind of vibe, and 20% of those rated it as great.
These vibes can be used on her or you, but their best use is between the two of you during face-to-face intercourse. Nestle it between her labia and let it give you both pleasant vibrations. Many women who find it difficult or impossible to orgasm during intercourse find it possible and even easy to climax with the addition of a small vibrator.
Some men feel reluctant about this, as if it’s a replacement for what they do. In reality, a vibe used this way is more of an extension of your body. How you move changes what the vibe does to her. With practice, you can tease her, thrill her, hold her off, and finish her off by changing position, movement, and vibe speed. You might also help her experience multiple orgasm for the first time.
Egg and bullet vibrators come in a vast array of sizes, styles, and prices. I suggest you try a low-cost model at first. The wireless models, which have come down in price recently, are nice since there is no cord, but be aware these usually use smaller batteries that are more expensive than the double A cells used in most corded versions.
The vibe pictured is a good choice for a first try. You can something similar here from Amazon (the page should be clean) but you may be able to find something similar at a drugstore and save shipping.
By the way: This is not a good “surprise gift”. Talk with her before you buy!