Amazon now has a free Kindle reader (beta) for the PC that duplicates the appearance of the e-reader's screen and automatically downloads any books you may already have on your 'bookshelf'.  It even displays the last page read on your portable device.  Sorry, you can not read magazines or newspapers.

I found that home-made materials (mobi files) may be read by right-clicking on the file and selecting 'open with' then 'Kindle for PC'.

It's a great way to put a toe in the water and test the Kindle experience.  And you don't have to actually buy a book.  They have a great many e-books that are free.

Amazon is raving about their Kindle sales so far and many other manufacturers are struggling to get on the bandwagon.