Resources to get started with Lua

[Megiddo]

Here's a list of links to help you get off your feet and get into Lua:

http://tylerneylon.com/a/learn-lua/ -- Learn Lua in 15 minutes (only for programmers familiar with the basics)
http://www.lua.org/pil/ -- Lua tutorial (written for Lua 5.0, but still works fine for 5.1)
http://www.lua.org/manual/5.1/ -- Lua reference manual for looking up specific functions
http://ulyssesmod.net/docs/ -- The ULib documentation
http://wiki.garrysmod.com/page/Category:Lua_Reference -- The Gmod lua documentation
http://www.tutorialspoint.com/execute_lua_online.php - Online lua shell, great for practicing what you learn and want to test. (No Glua(Gmod Lua) of course, but will help you practice basics)


_{[EDIT - JamminR] - 08/29/13 - Changed Gmod lua reference link
[EDIT - JamminR] - 01/21/15 - Added online compiler/editor}

[Megiddo]

Added http://tylerneylon.com/a/learn-lua/ which is a pretty fantastic reference.

[Timmy]

A great Lua tutorial for those with no prior programming experience: http://www.phailed.me/2011/02/learn-lua-the-hard-way-1/.

[iViscosity]

I know this is old, but a great site I use for testing Lua code is repl.it (https://repl.it/languages/lua). Let's you run it online so you don't have to compile Lua yourself. It doesn't support gLua, naturally.