Sprite Resources
Ever spent ages looking for a sprite but couldn't? Well, this is where you can get them. I shall link to some of the most visited spriting sites on the Internet :D
The Spriter's Resource
This is the big one. The Spriter's Resource has sprite sheets for a whole load of stuff. If you're ever looking for a sprite sheet, this is the first place you should look.
Veekun
This is another biggie. Veekun has massive sheets of Pokemon sprites from different games, and is currently the only site that I know of where you can get B/W sprites in a full sheet. This is a must visit for anyone who needs a sprite. Also, on their Pokedex, they have all individual sprites. Just click the link saying 'Detailed flavor page covering all versions', you can get them separately. :D
Pokemon Elite 2000
This site has lots of sprites from different Pokemon games separately, which makes it ideal if you want to use a Pokemon sprite quickly.
GTS+
GTS+ has sprites, Sugimori Art and more, so if you ever wanted to see the sprites from the different games together or wanted one to use, you should go here!
Project Pokemon
Project Pokemon is another site which is good if you need to use sprites from Pokemon Mystery dungeon quickly. It is a reliable site and is organised by alphabetical and numerical order.
Tutorials
Ever wanted to learn how to do a type of spriting, but never could? Well, this is the place to find some to help you out. :D
Chesu's Spriting Guides
From PokeCommunity, Chesu is an epic spriter who has made some tutorials on how to sprite. This is a must-see for all spriters, and he's always updating, so check back every once in a while, and he might have new tuts. :D
How to sprite
A little outdated, and some have been deleted, but this is a good starting point for beginners. Contains some basic spriting tutorials and is easy to follow.
The Spriting Cavern
These tutorials are easy to follow and are aimed at beginners. They are detailed and explain clearly, so this is another good place to start if you are looking to sprite.
The Cave of Dragonflies
TCoD is back, and with very in-depth tutorials. If you have time to read it all, this is a good place to go.
WIP.