I'll do this off the top of my head, episodes that don't leave an impression with me probably aren't in my top 20 anyway:
1) TRUTH BE TOLD / TRUTH TAKES TIME / THE TELLING
4) PHASE ONE
5) MIRAGE
6) ALMOST THIRTY YEARS
7) THE COUNTERAGENT / PASSAGE (II) / THE GETAWAY
10) ALL THE TIME IN THE WORLD
11) COUNTDOWN
12) PASSAGE (I)
13) BEFORE THE FLOOD
14) RENDEZVOUS
15) PARITY
Man, I took this way too seriously, I took like a half hour considering plot points/character development. I only managed to come up with 15, all the other episodes I liked were about the same, all above average. I just couldn't rank some of them relative to one another, so there are two ties.
Edited on 10/07/2006 8:34am
Edited 2 total times.