For Guardians of the Galaxy it really depends on how far back you want to go. The current group (movie group) really started in the event Annihilation Conquest and then continued into their series by Abnett and Lanning and concluding in the Thanos Imperative event. Then not that long ago the book was relaunched under Bendis with the current series (after having them show up in the first arc of Avengers Assemble). If you want to go back to the beginning with Annihilation Conquest... I'd recommend that. If you don't want to go back that far then I'd suggest starting with Bendis' run. If you want to go back even further prior to when they were a team, most of them showed up in Annihilation (note: separate event from Annihilation Conquest).
Spider-Man... I don't know. I've not read it since One More Day, but I know the title just recently relaunched. I think it's only a few issues in, so you might want to start there. If you want to go back further, I'd recommend starting with Dan Slott's 'Big Time' start, which was around Amazing Spider-Man 648 or something like that.
That's all I can help you with. I have no clue on the others. I think there's been a bunch of different White Tigers, but the most recent one (the teenage girl) started in Avengers Academy sometime. Maybe around issue 13 or 14... something like that.