The 'fake sex noise' cutaway scene was an absolute classic, one of several key standout moments I kept remembering long after my fragmented viewing patterns during Spaced's first airing. The character positioning of the scene, with Tim in the foreground engrossed in his PlayStation, and Daisy in the background jumping almost childlike on the sofa, was just (and still is) so damned funny - it stuck in my mind for ages afterwards. And the dialogue either side of this wonderfully brief cutaway sequence was a fantastic framing for what remains an iconic Spaced moment for me.
And as Zoe has rightly mentioned, the 2001/refridgerator homage, along with Field Of Dreams' "If we have it, they will come", and the Close Encounters homage at the foot of the stairs (preceeded of course by the brilliantly eery of "Join Us...") really drove home the fantastic otherworldliness of the series.
But as well as the brilliant movie homages of course, there are so many great character moments:
The first proper introduction of Mike:
Tim: "I think you may have missed the puppet show, though"
Girls: "Fuck Off!!"
Tim: "What did you say?!?!"
Mike: "They said 'fuck off'"
Tim: "I know what they said, Mike!"
(I just love Mike's pronunciation there)

Tim inviting Brian (I won't quote the entire, brilliantly mirrored exchange):
Tim: "There'll be girls at the party"
Brian: "Really?"
Tim: "Yes"
Brian: "Mmmmm..."
And of course, Marsha's catchphrase "'Ulloooo" to the paperboy at the very end. So many other moments to mention....
If I'm honest, I would say Episode 2 was truly where the series first fired on all cylinders for me.