DM Question: How do you make combat more interesting for players who turn it isn't?

I have two, sort of related questions.

1. My players sometimes complain that combat takes too long. Or more, they complain it takes awhile for it to come back around to their turn and while other people are going, all they're really doing is sitting and waiting. Now I know part of that is resolved by each of them figuring out what they should be doing on their turn and people knowing what they're doing on their turn should speed things up. But is there anything else I can do to make combat more interesting for players whose turn it isn't?
2. How do you feel about using abilities that basically remove a player from combat? Like the chasme drone ability basically takes anyone who fails that check out of that combat. And combat can take over an hour or more depending on what they're facing. So, that person just then has to sit there for an hour doing nothing? Or what about stun abilities? Or things like banishment? I want to use these abilities because I think it makes things more dramatic and I don't want to limit monster abilities, but I also want my players to have fun and sitting around waiting for everyone else to finish isn't fun. What do people think?