JAPANESE PAPERS
Japanese papers are generally of two types- Bristol type and blue-lined paper pre-ruled especially for manga. The former are almost always excellent, but unavailable throughout most of the US as well as mostly being sold by the sheet and uncut(a big hassle).
However, the blue lined type are insanely convenient; they make panel layout effortless and have consistently high surface quality. They are available in a variety of different sizes porportional to printed manga pages(which are NOT, by the way, porportional to the traditional 3x2 US dimensions for comics....) and the blue centimeter guidelines along the edge are non-repro. My only complaint is they are a little too lightweight for my liking; the heaviest I can find is 135 kg. It shouldn't be a problem if you take care of your materials. If you have a way to get these you should definitely give them a try.
to be added:Card Stock, Misc.