Hair Conditioner - fights more than split ends!
This problem of cemented nits has spawned an small industry of products claiming to dissolve the substance that glues the nits to the hair shaft. Sprays, rinses, creams - you can find many that claim to loosen or remove nits. Probably the most common home remedy that I have seen people use for nit removal is vinegar. Have you ever had vinegar in your eyes? The kids whose parents gave them a vinegar rinse are not usually appreciative of this technique.
As you may know, I feel the best way to remove lice, eggs, and shells is manually. I recommend using a good metal lice comb (with very rigid teeth, such as the Licemeister or the Nit Free Terminator). But I also recommend wetting the hair and slathering it in cheap hair conditioner. This process of wet combing is proven to greatly increase your chances of lice detection and it is a non-pesticidal and effective way to remove lice and nits. The conditioner helps the hair remain wet (slowing down the lice), makes it easier for the hair to stay detangled, and allows the comb to glide through the hair more smoothly. I always recommend the cheapest conditioner because you may need a lot of conditioner and beating head lice should never break your budget.
Interestingly, hair conditioner was part of a head lice study that came out this past spring. The study was called "Efficacy of Products to Remove Eggs of Pediculus humanus capitis (Phthiraptera: Pediculidae) from the Human Hair". You can read the study's abstract here. In other words, it compared different products that made claims that they removed lice eggs from the hair shaft. The conclusion? Egg removal was significantly helped with just water and hair conditioner. Specialty products were no more effective than these simple tools and some substances had no effect at all.
So, join me in buying that vat of generic conditioner from your local dollar store. This is just one more example of how effective does not have to mean expensive.