Some of the things we do with our tanks....
Solo world bosses / Champions *way* above your level (trying to, anyway): This one we use mostly for tanks that are leveling. spend 15 minutes with your heal companion just to get the bastard to 5% then you die....then you gotta go back.... try again. You learn to balance CD's and some INTERESTING ways to lessen damage.
Down-grading gear (ie: half-naked runs)
NiM KP: Solo tanking Jarg & Sorno, but split the DPS so it's REEEAALY fun for he tank
HM Mando Raiders: Tell the tank he is not allowed to AoE taunt with no straight line pulls. Basically he/she can single target taunt, but must LoS all pulls. Gets them in the habit of controlling packs and therefor controlling incoming damage (plus works on aggro building)
Karraga is your slow kiting test. :P
That only counts if you can kill him on the elevator so his corpse goes up and down