We've shared one tool that turns expands truncated RSS feeds, but free service Full Text RSS Feed Builder does an even better job: Just plug in a feed and it will give you a new one containing each article's full text.
If you're tired of RSS feeds only showing you the first paragraph or two of an article, Full Text RSS Feed Builder will give you a new RSS feed showing the full articles. It'll even turn aggregators like Hacker News or Daring Fireball into regular feeds, showing the full text of the linked article instead of just the link they usually show. It's completely free, doesn't add any ads, and keeps you from ever having to leave your RSS reader. Hit the link to check it out.