i use different types of hair for different braid/cornrow styles. i braid/cornrow myself. my fotki has pics of one brand. these are the ones i currently use:
1. human hair extensions (i don't know the brand) but it is a wavy texture
2. Tokokalon Yaki Pony by Sassy (http://www.sallyexpress.com/viewCategory.aspx?cid=129) this i use because it has a curl on the end and is very straight. it looks pretty when the braids hang
3. Janet Collection Braid Hair (this is my fave)
i use the jumbo Kanekalon (kinkier more realistic natural texture) for generic braids/cornrows esp when i do the Crown and Glory Braid Regimen (http://www.growafrohairlong.com/braidreg.html)
i use the Silky Yaki Braid for up dos or straight hanging braids. this is very straight in texture
remember some types of synthetic hair will not burn so you can't melt the ends of some types. ask the foks in the bss which ones plus it should say on the package if it is flame resistant.
the Janet brands i get like $1.00 per pack. The Sassy was $3.00 a pack. I have found for me I use one pack of hair or less depending on the style.
DON'T buy any hair that is 3/$1.00 or something like that. it will be crap! LOL