Note that AVR's can be programmed in Serial or Parallel modes.  This does NOT refer to the connection to your PC but to the connection to the chip. The  In-system-programming (ISP) that is discussed on this web all refers to serial ISP programming, whether the adapter attaches to the serial or parallel port of your computer.  Confused? So was I.  It is possible to use the STK500 to perform parallel programming but I have been unable to find any reason why you would want to.  (If you know - tell me.)

I have chosen to use the word adapters but these are often called programmers (which is confusing because the software is also called a programmer) or just cables.

Indeed you can just wire up a simple parallel port cable to the Kanda - STK200/300 standard and have it work using PonyProg or UISP.  All commercial products put some kind of buffer to protect your computer and circuit. Not all parallel ports are created equal and if you short the port on your laptop remember the disclaimer!  Also remember that all parallel ports cables are not the same.  It's quite easy to write your own programmer that turns port pins on and off - and several people have - so check to make sure the cable you are using is compatible with the programmer. 

What is the Kanda - STK200/300 standard? A history lesson.  Kanda used to make an adapter for Atmel that was marketed as the (then) AVRISP.   This used the same parallel port interface as used on the STK200/300.  This became a de-facto standard (sometimes referred to as the Kanda or STK200/300 standard).  Then Atmel dropped the STK200 & 300 and went to a serial port adapter as used in the STK500 and (new) AVRISP.  Atmel no longer supports the STK200/300 standard.

The STK200/300 cables can be made for a few dollars in parts or there are various commercial products.  The STK500 & AVRISP cost a lot more. ($130 & $45 CDN respectively)

USB?  My notebook no longer has any serial ports and this is a trend - the future is USB.  I have a USB - Serial port adapter that fakes a COM port.  USB Kits has a USB programmer but it's $140 US.  Given that Atmel sell USB chips and AVR chips one would expect that they'll soon have one available. and hopefully it'll be in the $50 range.