I mentioned in my druid vs. paladin tanking post that the one issue that people still seem to have with paladin tanking occasionally is that of mana management. The subject also came up in a WoW.com post the other day, and while the author's comments on it were technically correct, I felt that they were still kind of missing the point.
I'm not a huge expert on paladins, but I do have a frequently played paladin tank and a healer of every class, and with that experience under my belt I feel that it's safe to say that paladin tanks at eighty should never run out of mana. Levelling is a different matter as the poor pallies don't get many of their mana regeneration abilities until fairly late, but for a paladin that's running heroics, mana should never really be an issue. I don't remember the last time I had to stop and drink while tanking with mine. It doesn't matter if you're overgeared, it doesn't matter if your healer bubbles you, if you're struggling with mana then you're doing something wrong.
The main problem seems to be that some paladin tanks appear to be mentally stuck in BC, when spiritual attunement was their only way of regenerating mana. Nowadays paladins have more and much more effective tools at their disposal to keep their blue bar full, and they should use them. Seriously, forget about spiritual attunement. It's still worth the talent points, and particularly handy in raids - where ten percent of healing received is a lot, what with bosses hitting for gazillions of damage - but in five-mans it's nearly irrelevant these days. Personally I only really rely on three simple strategies to keep my mana bar full in instances:
1. Buff yourself with blessing of sanctuary
I cringe every time I see a paladin tank using blessing of wisdom or something else instead. Yes, BoW gives you some mana back, but it's only a static amount and has no other benefits. Blessing of sanctuary on the other hand gives you three percent damage reduction, ten percent extra stamina, ten percent extra strength, and a source of mana return that scales, namely with how many mobs you tank. If you need more mana, just pull a few extra (melee) mobs, and watch as all the dodging, blocking and parrying you do recharges your little blue bar in no time.
2. Keep divine plea rolling
Divine plea is pretty handy to begin with, what with allowing you to regenerate twenty-five percent of your mana over fifteen seconds once a minute, but with the protection talent guarded by the light you can theoretically keep it up forever, replenishing your mana bar from naught to full every minute. All you have to do is keep hitting things. I admit that this can be quite tricky when you're only just starting out, and if I had a penny for every time I went "argh, divine plea fell off" during my early tanking days I would have a fair amount of small change. However, this is simply something that gets better with practice. If your healer has mana and is otherwise ready, don't hesitate to pull the next group of mobs to keep your regen rolling. And well, if there is a brief break after that, the cooldown to reactivate divine plea manually should be available again anyway. Don't forget to use it!
3. Use consecration responsibly
It's an awesome tanking ability, don't get me wrong... but it's also a mana hog. Back in BC judging and consecrating was all paladin tanks could do, but these days they have so many other useful tanking abilities that consecrating on every pull really isn't necessary anymore, especially if you're only tanking three mobs or less. Hammer of the righteous, judging, shield of righteousness and any reflective damage are going to do just fine to maintain aggro most of the time, so use consecrate responsibly and save yourself some mana.
That's all that I usually do and it's more than enough for me, but if you're really desperate you can also use seal and judgement of wisdom for extra mana return.
Following these simple principles you can embrace any shields healers cast on you... and don't even think about taking off your pants in order to take more damage for spiritual attunement. Smart paladins wear their shields with pride and like to keep their pants on, thank you.