Personally, I'd recommend Martial Weapon Proficiency (Longbow) and getting a suitably strong, magically-enhanced composite longbow for your ranged weapon (a simple +1 composite longbow made for a 16 Strength should suffice, and you can probably get a handful of arrows with cold iron or alchemical silver arrowheads for those occasions where you need to deal with Damage Reduction monsters). If you don't just use a light crossbow with its single attack per round, anyway.
Other than the bow option, here are my feat suggestions. Power Attack isn't very useful for monks given their medium Base Attack Bonus and how much the feat favors two-handed weapons in 3.5.
Improved Natural Attack (Unarmed Strike) for your 6th-level feat (since it requires a +4 BAB), from the Monster Manual or System Reference Document's monster feats section (since monks can treat their unarmed strikes as natural weapons for purposes of improving them).
Stunning Fist may or may not be worthwhile for you, since plenty of melee opponents will have good Fortitude saves and won't be stunned often, plus some monsters are immune to it altogether. Improved Grapple may be a better choice for your 1st-level monk bonus feat.
Deflect Arrows or Combat Reflexes are both useful choices for your 2nd-level monk bonus feat, so take Deflect Arrows if you've run into a lotta enemy archers/javelineers/crossbowmen in your campaign (and thus expect to get shot at a lot with physical attacks), or Combat Reflexes otherwise.
Improved Trip is probably best for your 6th-level monk bonus feat.
So that leaves you with a 1st-level feat, 3rd-level feat, and 9th-level feat to choose, plus your human bonus feat if the character is human. Now, it's important to realize that as a monk, and with only 13 Constitution, you're not going to survive many full-attacks from monsters, fighters, barbarians, or the like. Tripping them with Improved Trip can help, but it won't always work, especially against the really big'uns and the quadrupeds or flyers.
I strongly recommend taking Spring Attack as your 9th-level feat, with Dodge as your 1st-level feat and Mobility as your 3rd-level feat. If you're playing a human monk, then use your racial bonus feat for Mobility and allocate your 3rd-level feat towards Weapon Focus (Unarmed Strike). You can take Improved Critical (Unarmed Strike) or something else later on at 12th-level, or Snap Kick from the Tome of Battle at 12th-level (Snap Kick can be used effectively with a Spring Attack!), and Bounding Assault from the Player's Handbook II later on at 15th-level to increase your number of attacks when using Spring Attack. The 18th-level feat could be whatever else ya like, maybe Improved Initiative.
