The main problem with the Monk is that it's difficult to put the class's weird abilities and immunities to effective use.
Here are some rather high level characters that our group is using that make some of the Monk's problems manifest. The characters are 15th level with 35 point buy for stats and standard equipment (200k).
Ran: Halfling Ranger 1, Rogue 14. Atts: +21/+21/+16/+16/+11. Damage: 1d4+3 + (1d6+1 electric) and 7d6 sneak attack. AC 29. HP 79. F: +13 R: +21 W: +11 Ring of Blinking
Orion: Human Monk 15. Atts: (flurry) +15/+15/+12/+9/+6 Dmg: 1d12+5. AC 29. HP 108. F: +16 R: +16 W: +18 Cloak of Major Displacement, Mighty Fist item +2
Practically, both ACs are 33, because both characters can haste themselves.
Without sneak attacking, Ran only does about one point less per hit than Orion. A rogue that is denied sneak attack damage isn't exactly the person you want around in a fight. And here we have a Monk whose damage is almost that bad (a Bull's STR on the halfling makes up the difference) and will hit less often.
Sure, a Stunning Attack is an excellent tool for the whole team, because both the rogue and monk have Expert Tactician. However, since the stunning attack has to be called in advance on one of the monk's attacks, and since each attack has a rather low chance to hit, the Stunning Blow attack will probably fail, even without taking the Fort save into consideration.
Want to be less stat dependant? Put all you got in Wis and Dex then take Weapon Finesse (unarmed). With 18 Wis and Dex, a 1st level monk has an AC of 19, far better than a 1st level fighter in scale+shield. He will be adding +4 to his attacks (+2/+2 with flurry). A 1st level human monk could even add Weapon Focus (unarmed). Or maybe Improved Initiative (which goes up to +8), attacking and stunning flat-footed foes. Or he could pick up Dodge and Mobility, which paves the way for a Spring Attack at 3rd level. With a rogue in the group, there's even more reason to pick up Dodge and Mobility. Not only your AC against one foe goes to 20 (24 vs. AoO for moving), you flank him easily, and the 1st level rogue then gets his sneak in with every attack.
The point on monk weapons is well-made. If your game has monks, it's only logical that you make magical monk weapons available. A monk that doesn't comission a +1 kama at 3rd level or so just isn't being very wise...
Somehow, I don't see a character that requires TWO 18s as stat independent. And, as others have pointed out, Monks don't qualify for either Focus or Finess at level 1, and can't take Spring Attack until level 6 at best since it requires +4 base attack. That simple +1 kama will probably require all the Monk's money at level 3 as well. He'd be better off commisioning a Pearl of Power for the wizard who casts Mage Armor.
Summon Monster 1 also provides flanking, and can appear next to someone, bypassing movement altogether.
I much prefer Psychic Warriors to Monks. First of all, Psi Wars have much greater flexibility because they get bonus feats and can select their own powers. Also, they can use weapons fairly effectively like most martial artist archetypes. They can also use powers like Deep Impact or Unavoidable Strike to actually hit things. Sure, they don't have poison immunity, SR, or great saves. However, most of the time, people interested in playing Monks aren't interested in killing the awesome wizard killer but crappy combatant.
