Allergic reactions, less-lethal chemical and biological weapons

Less-lethal approach, though not exactly nonviolent.

A significant segment of the population suffers from one or more allergies. The knowledge of such, gleamed from the target's medical documentation, may allow a disabling attack, with response ranging from a mild discomfort through a rash to a life-threatening and immediate hospitalization requiring anaphylactic shock.

The agent used, depending on the characteristics of the target, may be e.g. some food or an insect.

Spiking target's food with a pathogen may also serve as a less-lethal disabling attack. Salmonella (or, if we want a quick epidemy in a facility, a norovirus) are just some of the possible candidates. A real case happened in 1984, when a cult in Oregon attempted to influence the county elections by incapacitating the voting population in the area by contaminating food in salad bars; genetic forensics, identifying the origin of the pathogen strain used, then led to apprehension of the culprits.
http://en.wikipedia.org/wiki/1984_Rajneeshee_bioterror_attack

Another nasty thing is chloropicrin, also known as "vomit gas". Fairly toxic, but in low doses not too lethal; acts as a lachrymatory agent and causes intense vomiting. Used in WW1 as a chemical weapon; the small molecule penetrated the mask filters and its effects forced the soldier to remove the mask, leading to exposition to more lethal agents. The effect is virtually immediate - can start in as little as 10 seconds. It is commercially available for fumigation and seed and soil sterilization. Gas detection tubes for chloropicrin are commonly available as part of chemical weapon detection sets.
http://en.wikipedia.org/wiki/Chloropicrin
The vapors can linger in the contaminated area, especially if enclosed or underground, acting as an area-denial weapon.
There was a case I heard about years ago of a quarrel between two chemists. One then contaminated the other's office. When the police came to investigate, their dog vomited just by sniffing the door, then the cops followed the poor doggie's example after opening the door and bravely stepping in.

Yet another WW1 material is bromoacetone. A fairly powerful lachrymatory agent. VERY easy to make, frequently used for pranks by students of chemistry. So easy to make it can be prepared by accident when attempting to prepare something else; people often forget that the solvent can act as a reagent too (been there, weeped at the reaction yield).
http://en.wikipedia.org/wiki/Bromoacetone

A commercially available CS gas spray will however do a comparable job; there were numerous cases of shopping centers evacuated or partially evacuated after somebody used a tear gas spray there.
http://en.wikipedia.org/wiki/CS_gas
Rigging such spray can with a pyrotechnic cartridge could provide a tear gas grenade/mine, useful for e.g. non-lethal protection of a facility against intrusion.

A lot of other methods can be gleaned from Schneier's blog, especially from his movie plot terror contests.