Array extensions (LastElement, InsertAt, InsertRange, Remove, RemoveAt, RemoveRange, Clear, Contains, Equals, Copy, Append, Merge, Search, Filter): http://programmingsolution.net/post/JavaScript-Array-Extension.aspx
Array extensions : (copy, forEach, find, findAll, contains, distinguish, min, max, first, last, sortAscending, sortDescending, randomize, count, except, intersect, average, sum, union, safePush, getRandom, insertAt, remove) : http://www.thegrubbsian.com/2009/01/25/useful-javascript-extensions
Extensions of Date objects - datejs.js: (today, compare, compareTo, equals, isAFter, isBefore, isLeapYear, parse, parseExact, validateDay, validateHour, validateMonth, validateMinute, validateSecond, validateYear, add, addSeconds, addMinutesD, addMinutes, addours , addWeeks, addMonths, clone, getWeek, getISOWeek, setWeek, toISOString): http://code.google.com/p/datejs/wiki/APIDocumentation
copy, deepCopy, clone - http://oranlooney.com/deep-copy-javascript/