The Rails 3 Upgrade Handbook by Jeremy McAnally
Rails expert Jeremy McAnally (Ruby Inside's "Top Hitter" of 2008) has been interested in Rails 3 for a long time, and he's dropped a lot of time into producing the Rails 3 Upgrade Handbook, a $12 119 page PDF (no DRM!) e-book that runs through the ins and outs of bringing a Rails 2.x application up to Rails 3.0 standards.
Forgetting the 6 pages of cover and contents, Jeremy's Rails 3 Upgrade Handbook is 113 pages of awesome. The Rails 2 and Merb journey to Rails 3 is covered at a high level to start things off, but you're soon brought down to actually getting your Rails application upgraded to Rails 3.0. There are a few freely available blog posts out there that cover some of the topics this e-book looks at, but if you want a single "how to upgrade a Rails 2.x app to Rails 3.0" guide in one, and without any hassle, the Rails 3 Upgrade Handbook is a must buy.
Want to get a basic feel for how it looks? Jeremy has a PDF with some sample pages, but here are a couple of screengrabs too.. you should see it's a slick production:
$12 though? Is everyone just selling products nowadays? Well.. Jeremy first contacted me a week ago to get my impressions of the book and talk about pricing. He was first considering selling it at around $20 but I suggested he lower the price point - not because it's not worth $20 but because it's useful enough that everyone should feel good about buying it. Jeremy went lower than even my suggestion, though, so $12 it is.
If you're interested in Rails 3 and have experience with Rails 2, however, this thing is a good buy at $12 - it'll save you at least $20 of time's worth crawling through the documentation and 101 blog posts, though of course, you can still do that!
If you really want to get value for money out of Jeremy, though, you should also check out his Humble Little Ruby Book. It's free (readable online or as a PDF) and makes a great introduction to Ruby, ideal to pass on to your colleagues, kids, or whoever. If anyone's earned the karma to actually sell a product for once, it's this guy!