First and foremost, I'd say the number one way to increase your leveling speed assuming you're soloing and not getting power-leveled in any way is to increase your movement speed. In that light, I can make a few suggestions with various assumptions built in (assume you can afford respec costs a couple of times while leveling, etc):

Druid: Getting the Tier 3 feral talent to increase your cat movement speed. You can max this out like 9 levels before you get travel form. Avoid the Shredding Attacks talent, you won't be shredding much as a soloer. You'll want to get Mangle as soon as possible, followed by Omen of Clarity as soon as possible. The remaining (9?) points however you feel is best.

Hunter: Similarly to Druid, Tier 3 BM talent to increase your pack speed. Not huge, but can save you time. On a similar note, I've found a pet with Screech to be the end all, be all of leveling/grinding. It helps for mutliple targets and is great aggro generation/focus dump. Also, there's no reason not to put more than 41 points in BM. By the time you'll actually want 20 points in MM, you'll be respeccing for PVP or raiding anyways. I'd definitely go with Spirit Bond 2/2 and Frenzy 5/5. Some of the rest is up for grabs, depends on what you like and don't like.

Priest: Until you get Shadowform, you'll be using your wand...a lot. Believe it or not, Wand Spec is powerful and important. At the early level (10-15) it doesn't matter too much which you go for first, Wand Spec or Spirit Tap, but once you hit 40, you'll want to respec Shadowform and then your next 5 levels, I'd go back and grab Wand Spec again.

Mage: It's been a while since I leveled my mage, but even 3 years ago, AOE grinding was very effective (back in my day, we had to spec insta Arcane Explosion). It's my opinion that frost is the superior leveling build, especially toward the higher levels (when you can get all the nice talents for shatter, etc). A few things support this: frost tends to be more efficient, frost crits are instant and are less likely to go "unused", and your survivability will be quite a bit higher.

I guess he didn't make a post with all specs available, and I'd also favor ret over prot. Prot is good in some specific level ranges, much like frost blizzard AE mages, where you can grab quite a lot of mobs and AE grind(like plaguelands fields and stuff).

About the druid comment, I found that later on, it's good to come back and put 2points in shredding attacks, so you can Pounce > Mangle > Shred >Shred(if you get a clearcast), which does pretty damn good burst damage to start the fights. However many people don't bother stealthing between mobs and just run around pulling with FF and chain mangling, so whatever suits your tastes I guess.

Overall I'm not convinced of the point of this thread though, and it could very well fit into the Twinking Tricks and Alts thread since it's rather relevant. It's also not hard to find leveling specs when you go to your class forums, or wowwiki.

Prot is a very nice build for levelling as a paladin post level 30. However, I have no idea why he put 5 points into divine strength. If you are going into holy, you must go at least 10 for it to have any effect (for the uninterruptable healing talent). Either way, if you are levelling as prot, your healing comes almost solely from SoL or JoL, not via your healing spells.

Ok, I actually just looked at the rest of the paladin spec....say what? Is this a joke?

The major flaw in this thread is that the ideal specs for levelling are not ones with 61 talent points.

I'd submit that with the 2.3 Quest XP buff, Retribution is the more viable leveling spec. There is simply more XP gained by finishing quests rather than grinding now, and that lends itself to single target DPS. Sure, there are kill XX type of mobs quests that can be trivial with Prot, but only if they are melee types of mobs.

Also, Persuit of Justice is a great leveling talent. 15% increased movement (and mounted) speed available as soon as level 22? It adds up a lot over time.