Ooh, do we take this back to reading on mainframes in the late 70s?
For portable devices, I trialled an Apple Newton, but it was just too expensive for me at the time.
1993-2000 Mac laptops
2000-2005 Handspring Visor Prism (and those indispensable extension modules)
2005-2008 Palm Tungsten T3
2008-2010 iPhone 3G
2010+ iPhone 4, being couriered as we speak
Peanut Reader was the Palm ereader, and developed into Palm Reader and then eReader. Mobipocket was the best on Palm IMHO, but eReader beats it on iPhone.
The sad part is having to part with one's beloved gadget. I'm hoping there's a special place in Heaven for hard-working ereaders.