I don't own an Ipod, due to the fact that I have an inherant lotheing of anything apple related. Mac = evil. Just look at quicktime!
That being said, I do know a fair amount about the blasted things. Personally, if I were going to buy an MP3 player right now, i'd probably go with the creative labs Zen vision M. It's not quite as capable as the Ipod in some respects, but it is easier to use in my oppinion. http://creative.com/products/product.asp?category=213&subcategory=214&product=14331&nav=1
Of your Ipods, You basically have 4 types. The Newest ones, the Ipod video, which will run you around $400, The standard Ipod 30gb will run around $350, Then you have the 5GB ipod Nano, which is a smaller version of the Ipod, they run around $200 and are more portable. Finally there is the ipod shuffle which is a completely usleless piece of crap that is just a memory stick with a random MP3 player built in.
There are hundreds of dock accessories to use with Ipods. most of them consist of a cradle, a charger, and attached speakers of some sort. They all work, if you get one of the high end ones, you're basically just paying for better speakers.
As far as getting fromt he Ipod to the car, if your car is new enough to have an audio line in port, you cna plug in directly. (2006, 2007 models generally, or aftermarket car sterios) Otherwise, your best bet is the RF transmitter. Belkin makes one that works with any MP3 player. You plug it into the headphoen port, then tune your car sterio to the frequincy it is broadcasting at. The range is very short on it, but they work pretty well.
The main consideration for picking an MP3 player are how big is your music collection, and will you have a need to carry around video files? If you don't ned video, and can be content with only a few hours of MP3's, the Ipod Nano's are pretty nice, although evil by default.