As one of our guild's two resident tankadins, I've been spending a lot of time thinking about how to best interact with various dps classes. Basically, two big factors distinguish paladins from warriors/druids:
1) Most of our threat generation is passive, resulting from AoEs or being hit. This means that if you draw aggro, it's much harder for us (if our taunt is on cooldown or the mob is untauntable) to get it back.
2) We use mana instead of rage. Since we regain mana from being healed, the important part of this is that we need to be taking damage in order to produce threat -- even more so than a warrior, I believe, although I do not have a level 70 warrior tank to compare. Initially, it may seem like it's the other way around, since the link between warrior damage and threat generation is one step instead of two, but I believe that it is even more important for a tankadin to be taking damage.
A couple of things you might want to know: we start many pulls by throwing our shield, which produces a lot of threat on three enemies -- less if it misses one, never more. The shield moves in what I believe is a deterministic way, but it's not always obvious which enemies it will hit. Also, our taunt has a longer cooldown than a warrior's: 15 seconds instead of 10. Compensating for this: we taunt all enemies off a given ally instead of just one, and we don't need to be in melee range to do it.
With this in mind, here's a rough guide on how to interact with DPS classes:
1) Rogue: The worst thing that can happen to us is to have a rogue stunlock the main target. Because our threat generation is passive, we need to be getting hit to maintain aggro, and also having the enemy stunned means we are taking less damage. If you are a rogue and you want your tank to like you, don't stunlock the main target or really anything; you will have it stuck to you, and a quick vanish just means that your healer will die instead, because we haven't gotten a whole lot of threat on it. Obviously, stunlock can be useful for temporary mitigation, but be sure your tank approves. Meanwhile, the sap presents an interesting challenge, in that we have to make sure that the shield doesn't hit it. This is usually difficult, because the best way to do this is to sap something in back, which is harder. I usually facepull when sap is in effect, which of course means dps needs to back off a bit and the healer needs to be ready.
2) DPS plate: No particular ramifications. If there is a ret paladin, they should make sure to slap on a seal of the crusader (improved) which they were probably going to do anyway, and sanctity aura (same deal) -- both of these results in us doing more holy damage, which is most of our damage, and which via Righteous Fury means tons of threat. Life should be pretty easy with a ret paladin around as far as threat goes. For fury and arms warriors, no real special treatment.
3) Hunter: The hunter can do many clever things which will help us. Because we're weak on ranged, misdirect pulls will often come in very handy for line of sight; the holy shield has a 30 yard range, instead of 35 for shooting. Note that the hunter can MD you and then you can scamper out of sight for an instant line-of-sight pull. If you have a particularly excellent hunter, they can MD, give you lots of threat on the primary target, and then trap a secondary target. MD also obviously combines well with a sapped enemy for line of sight pulls.
Freezing traps present a problem for the shield. Optimal, obviously, is to not have the shield hit the freezing trap. If there are 3 or fewer enemies, or you don't know where the shield is going necessarily (I believe it jumps to the nearest enemy with ties broken by distance to you, it hitting the nearer one, but this may not be reliable and distances may not be easy to ascertain), this may not be possible. Hunters need to generate more threat on the target than they may be used to from warriors -- a Distracting Shot and a couple more hits should do the trick.
We have an advantage on trap resists, since we can taunt the mob back from afar; of course, if we threw our shield, the hunter can just feign death and we'll get the mob back.
4) Mages -- the shield throw is huge here. If you hit the to-be-sheeped mob with your shield, then the sheep will come to you if it breaks or is resisted, instead of the usual beeline for the hapless mage. I'm not sure how aggro generation for an enemy in sheep form works -- I think there is none, which means that if you have hit it with the shield, no matter how many times it's resheeped, it will likely come for you when it's done. Also, because the target is dazed, it comes for you slowly, which means the mage has plenty of time to sheep it before the mobs come into where you have placed the fight and will be concentrating. This is an excellent dps class for a paladin to work with, not even counting the oh-so-useful biscuits.
5) Warlocks -- warlocks can go more nuts with us than with warriors, because of the threat we generate on all the mobs. In particular, a warlock can usually get away with a DoT or two on each mob. Obviously, don't overdo it, but your tankadin should be able to hold threat with one or two torture devices in place. Banish is also a nice device, because you can consecrate through it. Seduction is quite iffy, on the other hand, because it's hard to maintain it in place since there is an interval in between and the mob is likely to run into our consecrate in the meantime.
6) Shadow priests -- you're in luck. Your Vampiric Embrace will no longer cause all the mobs to hate you. Also, when you mind control a guy and it fails, we're there to save the day instantly with a taunt. No need to thank us -- that mana we're getting back from VE is more than enough.
7) Shamans -- no particular notes, as far as I can tell. Mana spring totems make us happy.
8) Cats -- see rogues, minus comments about sap.
9) Boomkin -- no particular notes. It's worth noting that I haven't run nearly as much with the last three items on this list, so there may be ramifications I'm completely missing.