Nice to see that there's someone else on CAA taking the JLPT. Things have been so slow around here for a while that I seriously was not sure there would be anyone else.
There are some ways you can check your level online to try to figure out what level to take. Unfortunately there is nothing I've come across where you can just take a simple quiz and it will tell you which level you will or will not pass, but there are some self-assessment pages with checklists, and you check the items you know to get an idea of what percentage of grammar/vocabulary/kanji on that level you know:
http://www.tanos.co.uk/jlpt/levelcheck/http://www.mlcjapanese.co.jp/Level_Check.htmlI feel like there are some other ones besides these which I previously used, so you might be able to find some other level assessments if you look around.
There are also the official sample questions here:
http://www.jlpt.jp/e/samples/forlearners.htmlWith these, unlike the others, the JLPT site will tell you immediately whether you got the question right or wrong. Unfortunately the amount of sample questions is rather small, however.
Keep in mind that you only need to get about 50% of the questions on the JLPT correct in order to pass, so if you're looking at a level where you know 90% of the material vs. a level where you know 50-60%, it's better to study a bit and go for the more challenging level. [/played it safe the last two times]