To keep track of this growth, there's now a new webpage on the Netflix website, movies.netflix.com/subtitles, which is accessible via a link in the website's footer, via search (for "subtitle" or "caption"), or linked from the detail page of any title that has subtitles. Subtitles are supported on PCs and Macs, Nintendo Wii, Sony PS3, Google TV, and the Boxee Box. Netflix hopes to add Roku and Xbox 360 support for subtitles later this year.
If you want to specifically find content that has subtitles, look for the Subtitles button in the Netflix player on the PC and Mac, or look for Audio and Subtitles on the movie or TV show detail page on Netflix ready devices. It's important to note that these numbers do not include the subtitles already available "burned into" the picture for all non-English content, so the amount of subtitled content is actually much greater than you might think.