The cool thing about these levels is that the current top tier talents are now available to you. As noted by Chris in the previous leveling guide, you'll have access to the fun talents now like Crusader Strike, Avenger's Shield, and, um... Divine Illumination. Well, mostly fun talents, anyway. You can put those talents to good use in the Western Plaguelands, which is where you should head. Town criers in all the major cities will give you Call to Arms: The Plaguelands! which will send you off to Chillwind Camp if you're Alliance and to the Bulwark if you're Horde. Many Undead Horde players will recall the Bulwark as the curious area where they strayed too far and encountered Level ?? spiders and bears, and subsequently, death.
In your element
I recommend the Western Plaguelands over other zones of similar level such as Silithus and Winterspring for three reasons. The first is because Silithus is dreary, boring, infested with bugs and should only be visited if you have a penchant for getting sand in your knickers and a month's supply of Off!. Secondly, you are on the serious business of leveling, so it doesn't help to frolic in the snow or make friends with cuddly bears. Thirdly, the Western Plaguelands is plagued -- pardon the pun -- by a plethora of Undead.
Paladins are in their element in the Plaguelands. The zone the best place to make judicious use of Exorcism and Turn Undead. Exorcism gets upgraded at Levels 52 and 60, and The Skill Formerly Known As Turn Undead (Rank 3) powers up into Turn Evil at Level 52. You should also just have gotten Holy Wrath at Level 50, so you should be have a little fun when you get into a tight spot. Speaking of tight spots, some quests might be somewhat difficult, such as Scarlet Diversions, the immediate follow-up to Call to Arms for Horde players. The mobs are within close proximity of each other and have wide aggro ranges, making it difficult for classes without any means of ranged pulling such as, oh... Paladins.
Should you find that the initial quests in the Western Plaguelands prove to be more than you can handle solo -- despite the added utility of your anti-undead spells in your arsenal -- you can head to Felwood to finish off some backlog quests that will push you up past Level 52-53. Felwood is also an excellent place to quest because of Demon mobs. Very few people like Felwood, too, so you can quest undisturbed for the most part. When you have gained a level or two -- Hammer of GG (Rank 2) at Level 52, yay! -- you can head back to Western Plaguelands. You will be given the option to head to Winterspring from Felwood, but Paladins should feel right at home in the Plaguelands in all ways from role-playing to lore to improved gameplay.
The cold war
Level 51 is also a landmark Level because it opens up In Defense of Frostwolf for the Horde and The Sovereign Imperative for the Alliance. It's time to hit Alterac Valley. At 51, numerous quests in Alterac Valley open up and most can be done relatively undisturbed. Most give 9,550 XP such as capturing Graveyards or the Towers and Bunkers. Completing the daily PvP quest Call to Arms: Alterac Valley also gives excellent experience and all these can be done at the same time.
With a bit of luck, it's also possible to complete Hero of the Frostwolf and Hero of the Stormpike at Level 51. As a reward, Retribution Paladins can pick up the Ice Barbed Spear, which is arguably the best weapon for these levels; Protection (or even Holy) Paladins can choose the Cold Forged Hammer. The Honor you rack up along the way can be used to purchase gear to fill out slots when you finally hit Level 60 or saved for Level 70 items.
The chain of quests in the Western Plaguelands, from the cauldrons to Andorhal, will give rapid experience to push you to around Level 54, whereupon you can move to the Eastern Plaguelands to do more quests. In particular, Tirion Fordring gives a series of killing and drop quests, including Demon Dogs, allowing you to use more of your fun abilities. At Level 54, Horde players will be led to Nathanos Blightcaller, who sets off a chain of quests. Un-Life's Little Annoyances can be done at the same time as Blood Tinged Skies from Tirion Fordring. Alliance have a shorter series starting from Highlord Bolvar Fordragon which culminates in a quest to kill Nathanos Blightcaller. Both quest chains will award Sacred Protector, which is an excellent Paladin shield.
These are among the richest quest lines in the game and are worth doing not only because they give good XP, but because they delve deep into Warcraft lore that will become relevant again when Wrath of the Lich King finally arrives. The Argent Dawn will return in some form or other, and the floating citadel of Naxxramas which can be seen floating above Plaguewood, will move to Northrend. So while there are good quests and XP gains in Winterspring and Silithus, Paladins are enmeshed in the storylines in the Plaguelands.
Paladins gain no new spells from Levels 54 through 58 other than higher ranks of old spells as well as your first Greater Blessing. You should pick up a stack of Symbol of Kings to extend your viability in groups. It's also the one reagent you'll use extensively, since Divine Intervention is extremely situational. Level 54 is also significant in that it is the last time you will get an upgrade to Hammer of Justice, despite the fact that you have 16 Levels to go. If the quests in the Plaguelands aren't enough to take you to Level 58 (although they should), you can head over to Kalimdor to pick up some quests to push you over the hump. As soon as you hit Level 58, take the next bus to Outlands.
Outlands quests are numerous, rewarding, and grant extremely high XP. Heading to Thrallmar or Honor Hold is the best option for leveling, and Paladins can continue to take advantage of their unique abilities as the zone is teeming with demons. Other than the inherent dangers on a PvP realm -- Hellfire Peninsula is the Stranglethorn Vale of the Outlands -- the zone is an excellent place to level as it holds enough quests to rapidly take characters past 60. Itemization also begins to change in the Outlands, as most old world blues are replaced by quest reward greens. Paladins benefit greatly from the new itemization, with numerous plate rewards possessing a mix of Strength, Intellect, and Spell Damage.
Prudent Paladins should have slowly accumulated the materials necessary for their Charger through all those levels. Elizabeth has prepared a detailed guide for the Alliance as well as for the Horde on how to get your bag space-saving mount. It's possible to hold off collecting the mats until you hit Level 60 but it's considerably easier to collect everything you need over the course of nine levels, allowing you to undertake and complete the quest line as soon as it becomes available. Congratulations, you're now one step closer to the home stretch. As exciting as Level 60 used to be, a whole new world opens up at Level 70.