I’m a Kindle 2 owner. If you’re in the United States, you should definitely go for the Kindle (right now Amazon doesn’t sell Kindle to people outside the U.S.). Here is a comparison of it with the Sony Reader:

http://www.speedreaderxreview.com/kindle-2-0-vs-sony-reader-prs-700bc-comparison

Other than the free wireless access, more available content is also a very important factor. I know quite a lot of Sony Reader owners complaint that it is difficult to find some books. Amazon, on the other hand, provide over 300,000 books in Kindle format, and the number is keep on growing (I remember there is only 270,000 Kindle books when I buy my Kindle 2 two or three months ago).

Another great feature that Sony Reader doesn’t have is the text-to-speech function of the Kindle 2, which means I can "read" books without even holding or looking at the Kindle. Now I like to use this function when I’ve myself busy on some boring things, say when I’m on the step machine or doing some housework…

I remember I read this review when I decide to buy the Kindle 2:

http://www.amazon.com/gp/redirect.html?ie=UTF8&location=http%3A%2F%2Fwww.amazon.com%2Freview%2FR2DUM7S4XW06QN%3Fie%3DUTF8%26ASIN%3DB00154JDAI%26nodeID%3D%26ref%255F%3Dcm%255Fcr%255Fpr%255Fcmt&tag=moreinfo-po-20&linkCode=ur2&camp=1789&creative=390957

Hope it helps.