He's probably also looking at the name of this site MP3CAR, and making an assumption that's not all that far-fetched.
Mix, like 2k1 said, this is primarily a CarPC forum, but you can't be blamed for asking what you asked based on the name of the website you're at. With that being the case, summarizing all the above, right now you're quickest easiest bet would be to do exactly what you're trying to do... just get an mp3 player for your car.
Part of my job is testing digital media players, so you're in luck. I've used quite a few of them. There are a few questions you have to ask yourself to pick the right player...
1. How much space do I need (how many songs do you plan to have on it?)
2. What format is my music library in?
3. Are other functions such as photos/videos/FM radio important to me or is it primarily to get music into my car?
4. What other features ARE important to me for when I'm not in the car?
5. Do I hate Apple and everything they stand for?
6. Is the HU in my Toyota the stock one?
7. Do I want to have control of the mp3 player from the HU of my car (if the answer to #6 is "Yes", then you can skip this question).
8. What size player am I looking for? (physical size of the player itself).
9. How much money can I spend?
Go ahead and shoot some quick answers back to those and I can give you some choices.