I'd say the ENTIRE show is pretty memorable. However, there were a couple of moments:
Season 1 episode 7 "Counteragent"
Vaugh: Hey
Syd: hi. Talked to my mother, there's an antidote, I'm gonna go get it
V: How dangerous?
S: getting the serum? Nah it'll be easy. But I need to take some of your blood with me, okay?
A couple of days and you'll be doing wind sprints.
V: Be careful...
THEY HOLD HANDS...awww
V: Syd, I'm sorry. I'm so tired.
Also, lets not forget that there's no drug like adrenaline
ALIAS RULES!!!!!!!!!!!!!!!!!