What are the best ways to obtain other discipline powers as a psion?

[Hirax]

Erudite is typically the easy way to score discipline powers (except 9th level ones), but I'm curious if there's a method that would work for a regular psion.

Now, there's of course psychic chiurgery (http://www.d20srd.org/srd/psionic/powers/psychicChirurgery.htm), which allows you to impart any power to another. So if you impart chiurgery to someone you've dominated, you can then get them to use chiurgery to impart all powers that they know to you. But this is cumbersome, because of the exp costs involved, and the problem that you can't cast something if its exp cost would take you down a level. Even thought bottle use gets expensive, due to needing to use 500 exp to use the bottle itself. Edit: The other problem with this method, of course, is that you might get kicked in the face for claiming that in your backstory you plundered the knowledge of several level 17+ psions, and that it was done in such a way that it was basically free with regards to WBL.

Is there a better way?

[Dusk Eclipse]

Expanded knowledge is the easiest way I know of; but it has the lower than max power level issue and costs a feat slot. Other than that Hidden talent can give you a discipline power and extra 2 PP right of the bat; but it technically requires DM permission as it is a variant.

[sonofzeal]

There's a cheesy trick involving manifesting from a Dorje, but it's up in the "what damage does a DMG call" category.

Expanded Knowledge is usually your best bet.

[Mithril Leaf]

Adding Powers
Psionic characters can learn new powers when they attain a new level. A psion can learn any power from the psion/wilder list and powers from his chosen discipline’s list. A wilder can learn any power from the psion/wilder list. A psychic warrior can learn any power from the psychic warrior list.

Powers Gained at a New Level
Psions and other psionic characters perform a certain amount of personal meditation between adventures in an attempt to unlock latent mental abilities. Each time a psionic character attains a new level, he or she learns additional powers according to his class description. Psions, psychic warriors, and wilders learn new powers of their choice in this fashion. These powers represent abilities unlocked from latency. The powers must be of levels the characters can manifest.

Independent Research
A psion also can research a power independently, duplicating an existing power or creating an entirely new one. If characters are allowed to develop new powers, use these guidelines to handle the situation.

Any kind of manifester can create a new power. The research involved requires access to a retreat conducive to uninterrupted meditation. Research involves an expenditure of 200 XP per week and takes one week per level of the power. At the end of that time, the character makes a Psicraft check (DC 10 + spell level). If that check succeeds, the character learns the new power if her research produced a viable power. If the check fails, the character must go through the research process again if she wants to keep trying.

Research is good if you've got some XP to burn. And manifesting from another source isn't quite as cheesy as it sounds, you have to make a solid UPD check and it still takes a full minute. Good for low level utility stuff though.

[Amoren]

Can't you use the research option to lean any psionic power, mind you for the cost of 200 xp per level of the power and making a psicraft check? You have to pay the xp cost and research before you level, but once you do you can select to learn the psionic power as one of your normal slots. And yeah, it might be a lot at early levels, but 1,800 xp to pick up a level nine spell when you're level 18 or 19 might be worth it. Especially since you'll earn more xp to catch up with the party anyway.

[Mithril Leaf]

Can't you use the research option to lean any psionic power, mind you for the cost of 200 xp per level of the power and making a psicraft check? You have to pay the xp cost and research before you level, but once you do you can select to learn the psionic power as one of your normal slots. And yeah, it might be a lot at early levels, but 1,800 xp to pick up a level nine spell when you're level 18 or 19 might be worth it. Especially since you'll earn more xp to catch up with the party anyway.

Indeed. Those society mind ones from DSP and psychic warrior ones spring to mind.

[Gotterdammerung]

b4 you take expanded knowledge, check to see if the power you want is on any of the mantles. Tap mantle may be a better choice. Tap mantle will not give you an extra power known like expanded knowledge, but it will give you access to several powers at once. And sometimes that is better.

[Dusk Eclipse]

You need acces to mantles before you can select Tap mantle feat (so awesome for Ardents or mantled Psywars; but Psions are SOL)

[Psyren]

You need acces to mantles before you can select Tap mantle feat (so awesome for Ardents or mantled Psywars; but Psions are SOL)

Not all of them - Egoists have an ACF that gets the Life Mantle for instance. This would qualify them for Tap/Don Mantle.