I have made several tickets in AutoIt's Bug Tracker.
StringTrimLeftUntil & StringTrimRightUntil - Does what it says
StringLeftUntil & StringRightUntil - Does what it says
CalcPercent - Clean calculations
ArraySplit - Simply put, Converts an 1D Array to an 2D Array based on Delimiters (See the example if you want to know what it does clearly)
IsMgcNumPresent - Checks if a number is a present in a number (Magic numbers aka Powers of 2)
IniReadWrite - Wrapper for IniRead. Writes the "default" value to the Ini file if the key does not exist! Very useful to generate config.ini by just replacing IniRead with IniReadWrite
_IEWaitForTagText - Waits for a HTML tag to appear with the specified text
ConvertTime12To24 - Converts 12 hour time to 24 hour time, made while keeping _DateDiff's format in mind :)
IsWindowNotResponding - Programatically check for "This window is not responding" in AutoIt
InteractiveCoordinateSelect - Lets the user interactively select a point on the screen
Process UDF - Get both the output & the exit code of a command with a single line of code.
Experimental Maps UDF - UDF for Maps (the new alpha datatype)
TheDcoder's IRC UDF - Full compliance with IRCv3.1
_Translate - Simple translation library/UDF for AutoIt
DcoderBot - IRC Bot Base for AutoIt
Magic Number Calculator - (Discontinued) Converts magic numbers to constants.
History of AutoIt - as a timeline.
Arrays 101: All you need to know about them! - A nice documentation of the Array datatype in AutoIt.
Maps 101: All you need to know about them! - A nice documentation of the Map (currently in development) datatype in AutoIt.