CocoaDialog is an OS X application that allows the use of common GUI controls such as file selectors, text input, progress bars, yes/no confirmations and more with a command-line application. It requires no knowledge of Cocoa, and is ideal for creating frontends to shell and Perl scripts (or Ruby, or Python, or... etc).
SVEN This is one of the most precious tools for scripters. It greatly inhances the power of Perl, PHP and alike on Mac OS X.
And if you want to replace the "?!" icon with a custom brew, just place your .icns file to CocoaDialog.app/Contents/Resources and name it cocoaDialog.icns. (Version 1.1.3)