Yup, you pretty much can't go wrong with most of the season 3 & 4 episodes people have been mentioning. Those were the seasons that made the show wildly successful. Some later season's episodes I'd suggest that you could use are...
Season 5 Disaster
. An exciting bottle episode, featuring the entire ensemble. Some comedy, some conflict. Something that would be really easy to watch. Perhaps Time's Arrow
, from the same season. Another ensemble episode, with an engaging plot. The Next Phase
. A rather innocuous episode, but with an interesting plot, and the characters really shine. Timescape
is a good choice for that same reason