When Paul Graham wrote that the "list of n things" is a degenerate case of the essay, our first thought was "Wow! That's for us!" And we're going one step farther: we're recycling an old "list of n things" essay from last year.
Seriously, we've been thinking of revisiting 10 must-have Rails plugins for a while now. There is a place for lists like that, and the Rails plugin and add-on space has been moving quickly. We are always looking for better ways to do things, so we try out a lot of the plugins that come along. Our list of favorites—the ones that we use on almost every project—is almost completely different than last year's model.
There's one important change in focus: the plugins and gems that are solely related to testing are gone from this list. Of course, that doesn't mean we're down on testing. On the contrary, we built RunCodeRun because we think testing is so vital. We're saving the testing tools for the RunCodeRun blog; we'll be writing another degenerate essay there as a counterpart to this one.
There are numerous other plugins we use for special needs, such as PDF generation or attachment handling. But our favorites are the ones that we use on almost every project. So here they are, along with brief comments explaining why you want to check them out:
Don't reinvent the wheel! Use these plugins (or others like them), and definitely consider contributing to them if they fall short of what you need!