Spies tend to be pretty useful, if fielded correctly. Against regular units they go kaput, but if you know the enemy will be fielding a mercenary army or a bunch of natives against you. Stealth ability is always useful (sometimes I stick a couple of spies between the two towns to figure out what kind of army they have), but most armies tend to carry explorers, which tend to make stealth useless.
"Wisconsin Cheese should be in its own food group, and a significant part of every meal." -Jared Ribble
"Now that sir, is what I call a dead parrot!" -SmashNBash
"I find love generally ends in a restraining order." -Maffia
"One person cannot change the world; they can change others." -Christian Stillings
"Closed. HG > Any other site" -Cheesewiz