Quite possibly OpenBSD (sys-admin/net-admin).
Kernel hacker specializing in odd OS (OpenBSD, FreeBSD, the new Solaris distro, etc).
Ruby on Rails used to demand high compensation back in 2006.
Clojure and maybe Scala might be on the same spot where Ruby/Rails was.
Sometimes what it takes is to be the top #5 consultants in a niche field (i.e.: PostgreSQL guru)
I'm employed by an eCommerce vendor myself, so I'm sure I'd have an intuitive understanding of general architecture, but actually understanding the internals of a system as an outsider seems like a difficult proposition.
The only real hope of learning it though is to have a company that you work for use ATG, send you to training, and get you coding on it every day.
This is why there is such a huge gap between the demand and supply of this skill set currently.
But of course, rumours are unconfirmed.
I'm unsure regarding Scala since a few articles have risen regarding getting burned by Scala (Yammer) or plainly suggested that Scala may not be it (David Pollack, one of the Scala celebrities).
Having said that, knowing Java developers, most (not all) of them would definitely flock to either Scala or Groovy instead of LISP. Have you heard anything about Groovy lately? Yep, nada, cricket. The cool kids (Yammer, Twitter) are using Scala (to some extend) so there you go.
Clojure on the other hand has that "LISP" tales behind it (LISP programmers are like gods or something like that) and it runs on Java so that gives people some kind of hope and smile on their face or something.
I don't know if either would be in high-demand but you may want to look around and do a bare minimum, out of the thin-air, lots of grain of salt type of assumption:
companies_who_use_X/people_who_sang_X_tunes = ratio_of_X_demand
or something like that.
e.g.: 10 people love scala, 10 companies using scala = 1
e.g.: 2 people love Clojure, 5 companies using clojure = 5/2 = 2.5
Guess who gets a better chance of aiming higher salary? :D
Of course that's just out of my arse type of calculation (for fun) :).