What is the best car desk rig on the market? 

Try jeniko.com. Well built, well priced.

JWG

The Jotto deck tops are great. Many police departments use them. They are made here in Arkansas, so they have to be of good quality. You can't go wrong with them.

There you go, Chuck....now I just cant' help it.  I think Bob Harvey's 3-step ladder is better than your pipe & flange!!   Afterall, you can get extra use out of the ladder when you want to wash the top of the roof of your truck or van.  The trick with that little ladder is whether you can slide the passenger seat back far enough and get the laptop to sit just right.  Do you use that cutting board for slicing & dicing too?  

yep, it multi-tasks, but I don't use it in the vehicle. You can see my mobile desk here and I bought it from these folks http://mobiledesk.com/  but I do NOT recommend it.

The previous suggestions are more adjustable and cost less.  The ones from mobile desk.com just have a bent tube at the top, and you cannot configure it the same as the Jotto desk or Jenico.com.  I got mine to work OK but had to hacksaw to shorten the pipe and do some mods.

Tim, That looks fancy enough. Just remember, the longer the lower leg, the more wobble its going to create. Not good for the laptop. The jeniko I use was less that $100, and has very little wobble.
 

JWG

The base that mounts on the floor of that Ebay unit is not large enough - I assure you it is going to "flex" like crazy.

The one above has just one mount, to the seat bolt.  The "upgrade" one below has one extra stabilizer bolt, but that still isn't enough

The base on my mobile desk is huge compared to those, and I think it is barely adequate as it only mounts at one seat bolt but has 2 additional stabilizer points on a very thick plate of steel that is about 4" x 6".  It "works" but if I had it to do over I would get one of the other suggestions above.

If you look at the bases alone at Jotto they will cost as much as the Ebay unit, but at least it would function.