I have wrote about USB based PIC programmers and simple PIC programmers. It seems that with PICkit 2 coming out, it makes less sense to use other serial based intelligent PIC programmers. Still some of the users may already have those simple programmers and want to build their own intelligent PIC programmers. In that case, here are some recommendations.
1. Wisp628A: http://www.voti.nl/wisp628/
You can build this relatively easily. Actually back in 2005, I've built two of this on a breadboard.
The alternative firmware and software from Rob Hamerling's xwisp2 (http://www.robh.nl/picsoft.php) is my preferred choice. It is cross-platform and supports OS/2, Windows, Linux, Mac OS X and FreeBSD.
You can either buy the kit and build your own or create your own based on the information on the site.
2. Easyprog: http://www.embedinc.com/easyprog/
The author (Olin Lathrop) provides the hardware design, firmware and software sources.
You can buy the kit and assemble by yourself. I do not think you would like to buy the ready-made kit since PICkit 2 may be cheaper and better. Embed Inc also has the ProProg
(http://www.embedinc.com/proprog/index.htm) which is aimed at production and USBProg (http://www.embedinc.com/products/eusb2/index.htm) which is aimed at profoessional lab and benchtop use. ProProg and USBprog seem to be both well designed.
3. Kitrus also has some kits. http://www.kitsrus.com/pic.html
The price may not be justified now that PICkit 2 is out and at only US$35 (not including tax and shipment).
4. Microchip PICstart+:
Some of the sites have the clones but I think this is not easy to be built by hobbyists and its feature is not as good as PICkit 2 even though it is more expensive than PICkit 2.