Mike Tsao puts the fun back in defunct.

An In-System Programmer for Atmel AVR microcontrollers

We designed this programmer to be the one that always just works, and that never requires you to get up from your workbench to get another cable or contraption. Everything it could reasonably need is already on your desk or is already built-in.

Features:

• It’s small.
• It uses a micro-USB cable, which everyone has nowadays.
• It plugs directly into your target circuit’s ISP6 header. No ugly and bulky 6-pin ribbon cable required!
• It provides either 5v or 3.3v power to your target circuit, if you want it.
• It handles any I/O from 2 volts to 5 volts.
• It can program CPLDs and FPGAs over JTAG using XSVF.
• It performs USB-TTL serial translation with an FTDI-compatible cable pinout. Program your Arduino Pro or barebones Arduino!
• In theory, with a couple jumper wires and some 220-ohm resistors, it’ll program other AVR chips that use PDI/TPI interfaces. (Tie together TX/RX with the resistors, and use the exposed XCK.)
• It has a rescue clock (ECLK) in case you set your target’s fuses wrong and can’t reprogram without an external clock source.
• A couple more general-purpose buffered output pins are brought out in case you want to hack on the firmware.
• (Feature still in design phase) Popular bootloaders are built in and ready to flash to your new chips, with no PC required. Set fuses to factory default, install bootloader, pop right back into your Arduino, and get back to work!

Check it out on GitHub!

Update 4/29/2012: Dean tweeted about noncompliance with his LUFA license terms (thanks, Dean, for such an amazing library!). I’m still working out what’s left to do, but meanwhile here’s a copy of the license from one of the header files:

/*
             LUFA Library
     Copyright (C) Dean Camera, 2012.

  dean [at] fourwalledcubicle [dot] com
           www.lufa-lib.org
*/

/*
  Copyright 2012  Dean Camera (dean [at] fourwalledcubicle [dot] com)

  Permission to use, copy, modify, distribute, and sell this
  software and its documentation for any purpose is hereby granted
  without fee, provided that the above copyright notice appear in
  all copies and that both that the copyright notice and this
  permission notice and warranty disclaimer appear in supporting
  documentation, and that the name of the author not be used in
  advertising or publicity pertaining to distribution of the
  software without specific, written prior permission.

  The author disclaim all warranties with regard to this
  software, including all implied warranties of merchantability
  and fitness.  In no event shall the author be liable for any
  special, indirect or consequential damages or any damages
  whatsoever resulting from loss of use, data or profits, whether
  in an action of contract, negligence or other tortious action,
  arising out of or in connection with the use or performance of
  this software.
*/