So, what monsters should be Elite and Solos?

[Rechan]

The main thing is that solos need to be downgradable to elites and normal monsters so we can have liches riding dragonback.

Just set the dragon and lich a few levels lower than the party. If the XP for both equal that of the party's XP total (or perhaps a level or two above), I think you should be okay.

 

[Fallen Seraph]

Rich Baker in his blog mentioned another solo-monster: http://forums.gleemax.com/showthread.php?t=1036215

In our battles we took on a group of high-level helmed horrors coupled with a very nasty magical trap based on a monolith in the middle of the room, and then later fought a primordial hydra (a nasty solo monster).