Haha, this is going to be long because not too far back I'd done a rewatch - I have a list for practically each episode! Lol. Let's see:
Afterlife: Spike's joy at seeing Buffy, counting the days since she died, the "every night I save you" speech, how he's the only one she can talk to.
Flooded: his offer to "thin the crowd a bit" makes her smile, he's supportive in all the ways she needs at this point.
Life Serial: Spike trying to integrate Buffy into his world. It's genuine and heartfelt, if a little heartbreaking. The kitten poker scenes are hilarious. Also, just the way he looks at her when she scrunches up her face in disgust after a swig of alcohol.
OMWF: Everything
Tabula Rasa: One of the best Spuffy kisses ever. And you clearly see an attraction between Randy and Joan.
Smashed, Wrecked, Gone are all my favourite Spuffy rich episodes and I love each of them for showing a new side to how passionate they are as people. I love how explosive they are together.
Doublemeat Palace: Spike is genuinely trying to support/help Buffy because she clearly looks so unhappy. He offers help in any way he can.
Dead Things: I love their touching conversation after sex. I love the vulnerable light both characters are shown in. I love how Spike tries so hard to protect Buffy's interests. It's a heartbreaking episode for both, especially how she beats him up, but even in this darkest of episodes, I see love/yearning.
Older and Far Away: All the flirting and humour.
As You Were is probably my least favourite episode (both for Buffy in general, and for Spuffy in particular) because of how awful Riley's return makes Buffy feel, and how that makes her treat Spike, so this one not so much, but there are still sweet moments between them that I love.
Hell's Bells: Everything about their interaction!
Entropy: I love the extreme vulnerability we see with Spike's heartbreak. He's in tears as he's discussing his feelings about "this girl" (Buffy) with Anya and they come together for solace. I felt sorry for both Anya and Spike here, and it's gut wrenching to see how heartbroken he is.
Seeing Red is super difficult to watch but it's an episode meant to raise the stakes and portray life at its grimmest, from the shooting of Tara to the AR scene. Buffy admits she has feelings for him as Spike comes to apologize to her about the Anya thing. I still take comfort in the fact that Spike was horrified after his loss of control and it was a turning point for him, he leaves his coat behind and it's a spring board for literal soul searching.
Villains, Two to Go and Grave are inspiring from a Spuffy standpoint because they show how determined Spike is to change and will undergo any trial.