the Originals, of course, plus Oz, Tara, Anya, Dawn, and, on occasions, Faith, Spike and Cordelia.
i never really considered Angel and Riley to be part of the Scoobies.
Angel because he was too much of a loner when he was in Sunnydale, too much time spent on his own, he got used to that. i think his time with the Scoobies helped him learn how to work with others, prepared him for being part of the team in LA, but i defintely wouldn't consider him a Scoobie.
and Riley because he was too much of an outsider. he was, techincally, working for the enemy, the others didn't trust him enough to fully accept him as part of the gang. even Buffy herself kept things from him when her mom was sick.
Edit:
Spike was part of the Scoobies when it suited him, or when he thought he could be useful. for example, when Buffy was 'gone' and he was patrolling with the others, or looking after Dawn. also, in S7 when he had his soul, i felt that he was part of the team.
something he mentions in LA when he was asking Angel what theire name was makes me think that he thought himself part of the gang.
"So, what are we called? Just tell me we're not The Scoobies."
not a perfect quote, as i can't remember it off hand, but you get the idea.