I've noticed that I've had a lot of Google hits from search terms such as "What should a BM talent spec look like at [insert level here]". So I figured I'd toss out my idea of a leveling spec. Before I begin, note that I don't really believe there is "One True Leveling Spec" (although there are some that are better ideas than others) and also that you will respec at 70. The following spec is not one that I'd go waltzing into heroics and raids with.
A Pike-approved Leveling Beast Master spec is going to look roughly like this:
This build is going to give you plenty of pet uptime without gimping you should you choose to do some lowbie instances.
Now let's discuss why I did/didn't take some of the talents.
Bestial Swiftness: To be honest I don't see this as being a particularly useful talent once you get Dash/Dive, but it's a decent enough "filler talent" while leveling and certainly better than Pathfinding. (Do not let me catch you with Pathfinding.)
The Lack of Spirit Bond: While I can sorta almost see the case for Spirit Bond as a leveling talent, there are three big problems with it in my eyes: 1.) The amount of health it restores is miniscule, 2.) There are better places to put two talent points, and 3.) In the vast majority of cases, if something is killing you or your pet, it's going to kill you anyway and Spirit Bond isn't going to stop it. I have never found a need to spec into this talent. That said, it does have its devoted fans, so you decide.
Five Points in Frenzy: Many of you who have level 70 BM hunters, myself included, only have 4 points in Frenzy. The reason is because 4 points in Frenzy is something like 99% as good as 5 points in Frenzy (I can't remember the exact theorycrafting but it was something like that) and there are better places to put that last talent point. However, for a leveling/grinding spec, there's really not much of a better place to put that point so into Frenzy it goes. That said, I would also certainly approve of dumping that one point into Catlike Reflexes or maybe Animal Handler. I myself just have a thing for specs looking "clean".
The Lack of Animal Handler: Animal Handler gets a bad rap for being a noob talent like Pathfinding. "Increased mount speed? Noob!" What people forget to see is the increased chance to hit for your pet which is going to be an amazing DPS booster once you get into raids. At lower levels though, it's not needed.
Ferocious Inspiration vs. Catlike Reflexes: If you are going to be an exclusively solo hunter and are not planning on doing any instances anytime soon and are looking for maximum pet uptime then I can see taking Catlike Reflexes instead. Otherwise, Ferocious Inspiration is the better choice because it's going to increase the DPS of you, your pet, and everyone in your party. If you do opt for the Catlike Reflexes route, though, keep in mind that you're not going to be keeping that talent at 70 if you plan on doing typical end-game stuff. Because once you get Go for the Throat and a fairly high crit rating, Ferocious Inspiration is going to be up almost 100% of the time and it becomes the vastly superior talent choice.
Improved Hunter's Mark vs. Efficiency: This is sort of a debate for the ages among hunters of all levels. The general consensus is that one hunter in your raid should have IHM so the rest can take Efficiency. If you are leveling then you don't really have to worry about that and it's more of a personal choice. IHM is going to provide a sizable boost to your pet's attack power which will help him keep aggro; Efficiency is going to decrease your downtime especially with the recent mana-regen nerfs and the fact that you won't have Aspect of the Viper for a while. Neither is a bad choice and go with what you prefer. I myself have always chosen IHM, though, because I like the better pet DPS.
Your First Five Points:
A lot of people I know will make a hunter, level it to ten, and then ask me where they should put their first talent point if they're going into Beast Mastery. The way I see it, there are two right answers to this question:
Endurance Training and Lethal Shots.
Endurance Training is going to start you into the BM tree right off the bat whereas Lethal Shots is going to take a brief foray into Marksmanship to pick up an amazing 5% crit before you head into Beast Mastery. What it really comes down to is if you'd rather get the Big Red Pet as soon as you can, or if you're willing to delay it for five levels to give yourself a big crit boost. Both are acceptable goals in my eyes and as such I see either one as being the right answer. I myself have hunters that have gone both routes-- though to be completely honest, I think I lean more towards the Lethal Shots route myself.
I should mention that if you are brand new to huntering and have something like a cat or other low-armored pet, it might be more logical to head into giving him more hit points right away. But don't let that deter you from 5% crit if ya want it.
The Respec to 70:
So you've made it to level 70. Hooray! You want to stay a 41/20/0 Beast Master but you know that you've got a leveling spec right now and you want one that will get you into instances and then eventually heroics and raids. Well, as I said, I'm somewhat of the school of thought that there is no one true spec... but here's what a typical level 70 raiding BM hunter spec should look like:
Important things to note about the change in specs:
Endurance Training is swapped out for Improved Aspect of the Hawk because it's a big DPS booster and because in a raid your pet should not be getting hit; the tank will be. This is the same reason why you drop Thick Hide.
Improved Revive Pet: You don't take this while leveling because... well, your pet shouldn't be dying all that much. But things happen mid-boss-fights in raids where Shade of Aran will randomly target your pet or whatever and it's good to have IRP so you can get him or her back into the action as quickly as possible.
The points in Bestial Discipline, I feel, can be somewhat flexible; I only have one point in it but with my cat and my current crit chance, I have learned that that's really all I need. If you aren't sure, though, or if you are using a Windserpent pet, then you should take both points.
Animal Handler is a must. Your pet is going to be missing a lot as is when he fights Level 73 elites, any possible boost to his hit rating (because he doesn't gain any from yours, unfortunately) is going to increase pet DPS which will in turn increase Ferocious Inspiration procs.
Four points in Frenzy, as mentioned before, are really all you need.
If another hunter in your raid has Improved Hunter's Mark, you can take Efficiency. If you are usually the only hunter than once again, the choice is up to you. And again, I like IHM because it will help out your pet, the tank, and all melee DPS involved.
Keep in mind that this is a pure raiding spec. If you have just hit 70 and still plan on doing a lot of grinding or questing for money, you may opt to keep your leveling spec, or perhaps a mix of the two ("The Raiding Spec" but with two points in Thick Hide instead of Improved Revive Pet, for example, is basically what I've been using since 70 for that very reason-- although to be honest it's high time for a respec for me.)
Well, that should do it for now. Remember, what I have said here is just supposed to be a guide, and if you have your own good reasons for your own spec, then go for it. If you have any questions or comments, lemme know!
Edit: Znodis has typed up an excellent counterpoint to this post over at The Mystic Hunter. It is well worth a read for people who want to achieve the optimum spec for fast leveling/pet-aggro/no-downtime goodness. I should have clarified that the spec I presented here is not designed to fill that role; rather it is designed to be a very good all-around spec that will introduce you to a lot of the things you'll be seeing as a level 70 hunter, and will still be a good grinding/leveling spec. But take a look at Znodis' guide if you want to get much more in-detail with pure grinding specs.