I used to have K40 4ft. whips on my Jeep, and they got good reception. I know K40 sells antennas in smaller lengths though, a friend of mine has one on his Samurai. You might want to check out their website. www.k40.com Also, I know Radio Shack sells cell phone-like glass mount antennas that can be used for CB's.
I got a magnetic mount, about 18-24" flexible antenna at a truck stop for about $20. A good truck stop will have a good section for cb's. If you want something more permanent, but not too long, Firesticks are good and not too expensive. One good site is:
I haven't tried the glass mount/cell phone style, but others I know say they weren't worth .02 and took it right off. Bad reception as well as transmitting.