My suggestion is not to surprise her with her first sex toy. There really isn't one kind that is the "best," it's really all a matter of personal preference. For example, if she prefers clitoral stimulation, a bullet vibe might be best, or if she prefers penetration, a dildo would be best. Bring the idea up to her yourself and work with her to decide what she thinks she might like, and then try it out!
There is a
great adult toy store here in Chicago, and their website is very easy to navigate for shopping. It also explains a bit about the different kinds of toys, which will probably be good for you. If you work together to pick out a toy, she'll be happier with it, and it will also be a fun way to communicate with each other about what turns you on, which will help spice things up all on it's own!
That being said, just a few things to keep in mind. Jelly toys can only be washed with regular soap, and due to their porous nature, can't be completely sterilized. Also, any toy made with silicone can't be used with a silicone based lube, it will damage the toy. So, if either of those things could be an inconvenience for you, perhaps stay away from those toys the first time out. Good luck!