Any GPS datalogger that can provide logs in a standard format (NMEA or GPX) can work with any camera with a reasonably accurate clock that records "time taken" EXIF data (which includes every Pentax digital camera in existence to my knowledge.)
Camera clock accuracy requirements are dependent on how fast you're moving when geotagging - 2-3 minutes off is fine for hiking, not good at 60 mph. A few seconds off is bad if you're taking pictures from an aircraft.
I use an iBlue 747A+ and love it. There are slightly newer iBlue models out now that use the same MTKv2 chipset. I also sometimes just use my Garmin Oregon 300.
The basic workflow is:
Record a GPS track with the logger
Take pictures with the camera
When you get home, download the images from the camera to your PC, and also pull the log from the logger. (Special software is required for the iBlue and other MTKv2 loggers, I use the free and open source BT747 tool -
GPS Data Logger Software - BT747 )
Use geotagging software to tag the photos using the log, based on the position the GPS was at at the time the camera says the photo was taken. Most photo management software has this built-in now. I use digiKam as I'm a Linux user, I believe Lightroom and iPhoto support it. There are also free geotagging tools - there's a popular Windows tool, I think it's called Geosetter. BT747 may also have built-in tagging now.