Ah, the wig. My first question is which version are you doing? The anime long ropey curls? The manga with the Four Curls of the Appocolypse, or the Art book Curls that Eat your Head?
I've gone both 'believable' and 'well mostly accurate' and there's a lot of options. For the most 'realistic' you can find some really good spiral curled wigs online that you need only style bangs/fronts pieces into. If you want the long, contiguous curls...you're going to have to pick your method of insanity. And that will depend on which version you're doing.
After making, and hating my 'accurate' wig three times I spoke with some fairly well known wig makers/designers and they all agreed that to do the 'accurate' one you will need a LOT of wig fiber, a lot of foam core, and a lot of patience to assemble them all together. I add that you will need a LOT of hair pins and a LOT of tylenol, no matter how well made this will weigh a bit more than you'd like.
Once I know which you're doing I can run through the suggestions for that sort, so I apologize for being a bit vague at this point.
~I've gone to look for myself, if I should return before I get back keep me here!~
Costume list 2009: Finished
17 initially planned :: 15 completed :: 6 moved to next year
Costume list 2010: Started
6 from '09 :: 9 initially planned, now up to 22 total