We have Snoozer car seats for the boys, they love them SO much that they beg to go for rides. Our little guy, Pickles, had one brief incident of car sickness one time, but it was on a very windy road near Yosemite. Otherwise, no problems for either dog and they've been on long trips.
Also, I didn't like the tether that came with the Snoozer, so I replaced it with the much sturdier Pawrider.