Ok, I guess since you're a pally and all I could offer a few suggestions though I think Dothammer already covered the best ones.
Kurn's Tower (10-30ish) - You haven't completely outgrow this place - check out the last few floors of the basement. Easy kills with nice xp. Can usually stay here till 32 or so - but they start turning light blue down there by then.
ToFS (25-45ish) - Best if you bring a friend, someone who can snare would make it really easy but anyone that can help with dps would make this zone rock for you. Everything here is undead.
Unrest (15-30ish) - You can solo here and like Dothammer said knock out your Ghoulbane.
Lower Guk (35-50ish) Still one of the best places for a paladin to level. Again, better if you bring a friend.
City of Mist (35-50ish) - Yep, more undead. There's a few near the zonein - try those first to see if you can handle em.
Dulak (40-50ish) - Docks and Boats, you'll need to go here anyway to get your celestial spells, look for a cleric to join you - they'll be here doing their temp quest.
The Hole (40-55ish) - lots of undead once you get into the city. You'll need a partner or two to get there though.
For more information and tips visit the paladin specific sites:
Paladins of Norrath The White Cross Bonzz