The following is a complete listing of all proficiencies legal in Yogi's campaigns.  It pulls from many sources (listed below), includes a few created by myself (in blue, click to get description), but not every one normally allowed.  Look for the legend at the bottom for a full translation of marks.  The groups certain character classes can pull from are listed below, and multiclass characters can choose proficiencies from any legal category:

Fighter or Barbarian - General, Warrior
Ranger - General, Warrior, Wizard
Paladin - General, Priest, Warrior
Cleric - General, Priest
Druid - General, Priest, Warrior
Mage or Specialist Wizard - General, Wizard
Thief - General, Rogue
Bard - General, Rogue, Warrior, Wizard
Psionicist - General, Psionicist

* = specialization field must be chosen
^ = specialization field may be chosen, or general at additional -2 to check
@ = non-standard grouping for Yogi's campaigns only
# = Planescape only

Sources (source number - page number)
1 - Player's Handbook (black cover with barbarian smashing in door)
2 - Player's Option: Spells & Magic
3 - Player's Option: Skills & Powers
4 - Planewalker's Handbook
5 - Complete Ranger's Handbook
6 - Complete Paladin's Handbook
7 - Complete Barbarian's Handbook
8 - Complete Thief's Handbook
9 - Complete Bard's Handbook
10 - Complete Wizard's Handbook
11 - Complete Psionics Handbook
12 - Complete Druid's Handbook
13 - Complete Book of Humanoids
14 - Complete Book of Dwarves

Special Notes and New Proficencies
Alter Spell
        Believing that magic is a highly unique skill, this skills was born.  It has two very different uses for the personalization of a wizard spell caster's magic
        First, a spellcaster may use this proficiency to make a spell that he is casting have a minorly different sesory effect.  A successful check can make a Fireball look green, magic missles scream like bottle rockets, cause a chill touch to make the hand look glowing blue, or make a wall of fod smell like a dead herring.  This will have no numbers effect or make a dramatic effect in the game (unless your opponent fears the smell of herring).  In the DM approves the use, a proficiency check is attempted during the casting.  If successful, the effect happens, but if it fails, the caster has screwed too much with the magic, causing the who spell to fail.
        The other use is a more permanent effect.  A wizard learning a new spell may use this check to alter the spell with greater impact in the game.  This could include making a fireball into a coldball, making magic missle into one singular missle with the correct total damage, or turn a Cone of Cold into a Cone of Noise.  Again, the change must be DM approved, with significant changes requiring a more severe penalty to the check, and it requires a check while learning the spell.  A failed check is treated as a failed learn spells roll, causing the caster to have to try again next level.  This adjustment is a permanent change to the spell, and can not be changed back again.  This can also be done to a spell already know, but it creates a new spell to be counted against the wizard's limits (from Intelligence).

Cantrip
        Similar to the first level wizard spell of the same name, it has the same effect, but is far more useful to a spellcaster.  A cantrip is a minor magical effect, such as a small glowing ball, the spark to light a pipe, or causing someone to feel a minor itch.  Either way, this effect is so minor that it can cause no damage, and lasts only as long as the spellcaster focuses on it.  The slot cost is one for a wizard, two for a partial spellcaster (such as a bard), or three for a non-spellcaster.  The check modifier is zero, minus one for each previous use of the proficiency, and minus two for each failed check.  These modifiers only count those uses within the last 24 hours.

Know Sigil
       This proficiency was suggested to me at GenCon, and I like the idea.  Sigil is one of the most compact, busy city in the multiverse.  Now, while most people might now how to find the Hall of Information or the Prison, but to know how to find the Styx Oarsman or Imeal's Happy Tounge, a body must know Sigil well, and navigation in the berg's streets can be a challenge.  A cutter with this proficiency can find all major locals in Sigil with no check, and might even know a city portal to save time.  A check would be called to find any particular place they know of.  It would also give some knowledge about most local laws and local personas.  This proficiency gives the cutter the knowledge of the average tout.

Modern Languages
Allowed Languages for Prime Campaign

Common	Dwarvish	Elvish	Elvish (Grey)
Halfling	Goblin	Gnomish	Orcish

Additional Languages for Planescape Campaign

Planar Common	Archon	Asuras	Baatezu
Bariaur	Bladeling	Dao	Djinni
Efreeti	Eladrin	Formian	Gehreleth
Githyanki	Githzerai	Guardianal	Inner Planar Trade
Khaasta	Lower Planar Trade	Marid	Modron (2 slots)
Night Hag	Rimilari	Slaad	Tanar'ri
Yugoloth

A general modern language proficiency is available, and those at the stats listed in the main chart.  If you want an unlisted language, you better give me a DARN good story for it.

Orison
        This is very similar to the above Cantrip proficiency.  The cost is 1 slot for a priest, 2 slots for a paladin or rangers, or three for non-priest spell casters.  It varies in that it has no modifier at first, but later a -1 for each time the proficiency has been that day, and an additional -2 for each failed attempt that day.  Otherwise, it makes effects as listed in Player's Option:Skills & Magic under the spell of the same name.

Planar Heraldry
        So much in the multiverse is based upon beliefs, and people often show these beliefs by joining a group and displaying that symbol.  However, not every faction of sect is well known.  Therefore, a person with this proficiency has studies these symbols and philosophies.  It allows a body to recognize a faction symbol in Sigil on sight without a check.  Any other sect requires a check, but success means knowledge of the group's name and basic belief system.  The better the chech is made, the more knowledge is gained.