Are there any Star Wars vehicles that have not yet been produced in a Lego kit?
As far as I know, all of the most common vehicles have been produced, but I could be forgetting something. There are many obscure vehicles which have not been produced, but I don't see any reason to try to list them all. Some examples would be many of the pod racers from Episode I, many of the hundreds of vehicles shown on Coruscant, or several of the speeders seen in the Mos Eisley approach in Episode IV.
The most notable vehicle that I can think of that has not been produced to my knowledge are the Royal Cruisers from the prequels:

Update:
I had previously been mentioned the Nebulon-B Frigate featured in Episode V and VI:

The Nebulon-B has now been produced: