Contagion is an amazing Episode.
It's really cool to see the enterprise's sister ship and I always wished we could see more of Captain Donald Varley. The guy who played him seemed like a fine actor! He made me care about him and his ship with a few logs.
I also always wanted to see more about the Iconians. They seemed like badasses. I haven't yet seen the DS9 episode that references them, but I plan on it soon. (Actually I probably did see it years ago but forgot all about it)