paladins now, since 3.0, get 30% spell damage from stamina. ie if you have +100 stamina you will get "for free" 30 spell damage. Paladin tanks now itemize exactly the same as warriors -- get enough defense to be capped (not sure what it is from 70-80, but you will need A TON -- like close to 600 i think?), then just focus on stamina, strength, and dodge/block/parry (avoidance). It makes no sense anymore to ever enchant, gem, or seek out items that have +spell damage -- you will get PLENTY automatically from stamina.

For example I just picked up at level 74 yesterday a very, very nice tanking weapon http://www.wowhead.com/?item=44735 - easy 5 minute quest you can do with a team. I picked up slow axe because it helps hammer of righteousness blows, some tanks will prefer the faster mace (imo the mace is more for warrior tanks but up to you). I was wearing the s2 spell dmg mage up until then, since I didn't really have a good "warrior tank" weapon, but the new axe is far and away better at helping me get threat.