I would like to do full-text searching of data in my Ruby on Rails application. What options exist?
It depends on what database you are using. I would recommend using Solr as it offers up a lot of nice options. The downside is you have to run a separate process for it. I have used Ferret as well, but found it to be less stable in terms of multi-threaded access to the index. I haven't tried Sphinx because it only works with MySQL and Postgres.
I would recommend acts_as_ferret as I am using it for Scrumpad project at work. The indexing can be done as a separate process which ensures that while re-indexing we can still use our application. This can reduce the downtime of website. Also the searching is much faster. You can search through multiple model at a time and have your results sorted out by the fields you prefer.