this might change depending on what class you are, but if your "use and lose" (as in they break/lost usually) dart user, you'll want to go with the highest natural DC stuff (note, if alchemist they can up the DC in many various ways) so (assuming I remember ability damage correctly) most 0 physical stats either kill or disable you. Injury with high DC is good.
Two main choices being, stack a crap ton of Drow Poison in an inhaled smoke stick like item (a ton of them make high DC) or for injury induced i would go with a low dex or str damage. Yes con damage makes them die faster and lowers the DC for later but it also costs a crapton more. 2saves are better than one, but also very costy sadly
Giant Wasp poison, Large Scorpion Venom, do good dex and str damange respectivly for pretty cheap. If your not too concerned about the save (i.e. poisoning say spell casters or other lower fort save) Blue whinnis can pretty much kill a spell caster on the cheap, or at the least take them out of the fight; the save is a bit sad but an alchemist can get some good usage out of this.
The three there are fairly cheap and effective poisons for the 3 main stats. There are some mental stat point poisoners that are pretty good, but I figured in battle you'd like something that helps your side more readily (lowering the other sides battle ability).
If your a dart lover, and have extra feats you could look at "adder strike" and "pinpoint poisoner" feats, they are rather fun.
Deathblade and
Purple worm poison is great, 2 saves, 1d3str poison 24DC, bit more expensive but a good gang for the buck
