Tall and skinny - tough one. You'll probably end up in something with more volume than would be ideal but that's not such a bad thing, especially for a beginner. My advice would be start by looking here: CKS| Whitewater Kayaks: Rodeo/Freestyle Kayaks, Free Running Kayaks, River Running Kayaks, Creeking Kayaks
. CKS just does a good job of providing information about their boats. That site or the manufacturer site often have info on max inseam, which will be the size problem you'll run into. I think for most boats you'll end up getting the largest one to fit your legs. I would get something in the "Free Running Kayak" category if you are an aggressive beginner or "River Running Kayak" if you are a less aggressive beginner. This site (mountainbuzz) is a good place to find used gear.