This is just a list of interesting and useful links in Newgrounds...

NG related:

FAQ
NG Staff

Submit content
Flash API: Keep track of your submissions, and make money running ads in your flash! Also be sure to read the Flash API FAQ.

User Pages - Some Ground Rules

How to help Newgrounds: Do you want to help Newgrounds? Then read this useful guide!

Working on your whistle status? Why don't you read these 3 guides? You can also find abusive reviews and submissions here.

Need your Flash deleted?

Get Flash player: Needed to watch Flash movies and play games.

Ideas for Newgrounds' Evolution MK3: Have an original idea to improve Newgrounds? Post it here!
If you want to discuss about ideas that are posted there, do it in this thread: NG Evolution Discussion.

NG Screenshot archive: Here you can find a huge collection of old pictures from the time. See how NG was back then before the redesign, as well as many other interesting things...

BBS related:

Forum rules: Read before posting. Also be sure to read the collab rules, the Art forum rules and the Audio forum rules.
Ng Bbs Houserules: Most of them are common-sense rules, but a lot of people lack of common sense.
Corky52's Guide to the BBS: Pretty interesting and useful.
Bannable posts & BBS Rules ala Zerok: This is a Zerok's post, those are his modding policies and thought processes, but since they are common-sense things, I suppose most mods do the same, so you should read this.
Guide: what is and what isn't spam?: If you're not really sure of what spam is, you really should read this.
Forum Rules, Clarified: It contains a message from the mods, and also extra information about several forum rules.

Guide to Bumping Topics: Read before you bump.
Official topics: Self-explanatory, you should read them, some are very important.

Rage's gift to you: Abusive reviews: Share the abusive reviews you find so everyone can flag them!

How YOU can become a MOD!: Wanna be a mod? Read this.

On to flash related things:

The newest (and best) flash version is Adobe Flash CS4, you can get a free 30 day trial here.

AS2 tutorials.
AS3 tutorials.
Animation tutorials.
Other flash tutorials.

Animation: Main.

Audio related:

Here you have lists of Studios & Editors, Software Synthesizers and Sound Converters.
For more resources go here.

Useful clubs and crews:

Review Request Club: Need reviews for your flash? Ask for them here!
The Pre-portal Review Crew: Go here if you need reviews for something unfinished/not submitted yet.

Not NG related:

Computer Hospital: Part Two: If you have a problem with your PC, whether it's a virus/spyware/adware etc issue, or perhaps you would like an opinion on which piece of hardware is best; that is the place for you.

Useful blogs:

Corky52's Guide To Writing Helpful Reviews: If you want to work on your reviews, but you don't know how, go here!
Corky52's Guide to Abusive Reviews: This guy is so awesome that he even made a guide to recognize abusive reviews!
Corky52's Guide To The BBS: Yes, another one from Corky52, based on this mini-guide from gumOnShoe
Helpful Wi/Ht? Threads, by sonofkirk.
Handy musicians' blog posts and threads: Go here if you're interested in making/submitting audio. Great blog made by Rig.
Reviews/Review Modding: kidray76 talks about the reviews and the guidelines in this awesome news post.
Flashback, Helpful links *as usual*: True, this news posts made by Insanimation also contains things about his life and stuff. But it also has helpful stuff and more interesting things you should check out.

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Last updates:
9/24/08:
-Made this section
-Added the Ideas for Newgrounds' Evolution MK3.

10/25/08:
-Added NG Evolution Discussion.
-Made the "not NG related" section, which currently has the Computer Hospital: Part Two.
-Added the "audio related section".

11/10/08:
-Added Forum Rules, Clarified.
-Dates here are now shown in the American way. Ugh, it looks horrible.

16/12/08:
-Added the "Useful Clubs and Crews" and "Useful Blogs" sections. Some of the blogs are twice on the list, but I still wanted to make a category only for them :)

23/12/08:
-Added this and this.

1/11/09:
-Added the NG Screenshot archive, and Flashback, Helpful links *as usual*.
-Hybrid-Of-Souls helped, so he's on the list of people who contributed to this.

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Want contribute to expand this list? Just leave a comment!
People who have contributed: mwmike and Hybrid-Of-Souls.

Cheers.