[paegus]

/*
 * Double Jump
 *
 * Description:
 *  Allows players to double-jump
 *  Original idea: NcB_Sav
 *
 * Convars:
 *  sm_doublejump_enabled [bool] : Enables or disable double-jumping. Default: 1
 *  sm_doublejump_boost [amount] : Amount to boost the player. Default: 250
 *  sm_doublejump_max [jumps]    : Maximum number of re-jumps while airborne. Default: 1
 *
 * Changelog:
 *  v1.0.1
 *   Minor code optimization.
 *  v1.0.0
 *   Initial release.
 *
 * Known issues:
 *  Doesn't register all mouse-wheel triggered +jumps
 *
 * Todo:
 *  Employ upcoming OnPlayerRunCmd function to remove excess OnGameFrame-age.
 *
 * Contact:
 *  Paegus: paegus(at)gmail(dot)com
 *  SourceMod: http://www.sourcemod.net
 *  NcB_Sav: http://forums.alliedmods.net/showthread.php?t=99228
 */

Original Thread

Get an updated version with less OnGameFrame and more updated syntax down here courtesy of Grey83