Personally, the only use for weapons my monk has found is using the ones that grant bonuses to disarm (sai +4) and trip (kama +0). At low levels, you can simply make them masterwork and gain the additional +1 to attack, since these two abilities do not do actual damage.
Furthermore, boosting your damage class up by one size by making copious (ab)use of the enlarge spell means that you're even less likely to want to use a weapon otherwise. (You tend to find interesting uses of the monk's unique ability to jump high while having his normal weight multiplied by 8.)
If monk weapons are to be a viable alternative to fighting empty-handed, then they need to be able to do more damage in the hands of the monk, or the monk needs optional feats that allow them to use their weapons in interesting ways.
Monk ability: Quarterstaff expertise
Example 1: A monk with at least 5 ranks in acrobatics can use a quarterstaff to gain a circumstance bonus of 5 moving through a threatened square by using it as a springboard device.
Example 2: A monk may perform an acrobatics check and a single attack at a minus penalty to trip two enemies in two adjacent squares. The monk must move 5 feet in order to do so, as this is represented by the fact that the monk essentially cartwheels to strike. The monk must threaten at least one in the first square and must threaten at least the second one in the second square. This draws attacks of opportunity. Failure to avoid
Monk ability: Kama expertise
When using a kama (or sickle), a monk may make a ranged touch attack at a -2 penalty to attempt to undo fasteners on armor. A monk must make a number of successful attacks equal to that of the base armor enhancement of the target. Certain types of armor are immune. Failing an attack in this manner disarms the monk.
Monk ability: Shuriken expertise
Example 1: A monk can throw as many as six shurikens at one time, at a -1 to attack per 2 shurikens thrown at a time. You may target only two opponents at a time, and if targetting two, the maximum you can throw at one enemy at a time is 3 shurikens. At level 12 you can throw up to 9 at a time at a minus 4 to attack, and at level 16, you can throw 12 at a minus 6 to attack.
Another mistake I think for monks is that they can't use longbow without taking a feat to do so. How infamous are Asian archers? I'm sure every monk out there relishes the idea of removing his bracers of (nat) armor so he can wear his bracers of archery, lesser.