This thread will be dedicated to JLPT information, and resources. A running FAQ from those who don't to (hopefully) those who've been there before. Feel free to add links, and dispute information given.
The JPLT is the generally stadardised test of Japanese ability in the fields of kanji comprehension, Listening comprehension, and Reading and Gramma comprehension. Speaking and writing are not tested. There are currently 4 levels, 1 being the hardest. 4, the easiest. Although in 2010 this is set to change to 5 levels. An extra level between 2 and 3, as this was quite a leap.
Ok, as promised (and earlier than expected) here are some links and pages to potentially useful information regarding the JLPT (Japanese Language Proficiency Test).
http://en.wikipedia.org/wiki/Japanese_Language_Proficiency_Test - Wikipedia, because everyone should look there fairly early into researching anything. If only for fun. Also has information regarding locations in many countries where one might sit this examination.
http://www.jlptstudy.com/ - A website devoted to study for stages 4,3, and 2. I haven't looked too deeply into the site yet, but it would seem to me that anyone concerned enough to name their website "JLPTstudy" probably has one aim in mind.
http://www.jlpt.jp/e/ - The offical page for the exams. Again, I've only breifly looked at the page, but as it has the word "offical" pastered all over the site, it's probably a crediable source.
http://www.jlpt.jp/e/about/sample.html - Actually this is a page from the previous site, but since it has downloadable PDFs with practice exams on (I haven't looked there yet, expect more information when I've taken a peek) I thought it might be useful for other people to check out.
http://www.jlpt-kanji.com/ - As you might expect, this is a site dedicated to the kanji necessary for each level. I'm unsure about how correct each list will be, as even in my somewhat limited study of Japanese I've come accross a number of sources claiming that X is the kanji needed for each level, and no far no two have agreed exactly. To this end you may notice the wikipedia page only gives rough estimates on numbers needed. It may will be (and it seems likely) that the number, and particulares vary from one exam to the next.