I wrote my first blog entry on this topic, and my second...
here's what I wrote, which includes what folks have said here, and some other stuff (and missed some other ides):
http://www.enworld.org/forum/blogs/janx/300-making-combat-faster.html
some extra toughts I have, since writing that last year, and reading some more ideas (you can never have too many ideas on this problem):
include monster stat blocks in your adventure notes. I write my own adventures using Word, and copy paste from the SRD. WHen I run from my laptop, I include the hyperlink to d20srd.org as well. This makes it easier to know your monsters, and not have to open up the MM.
force players who take too long to lose a delay action, and then lose a turn. This is comparable to the "dithering" rule. The main point is, you can't take forever in a real combat to decide. You could rule they go into "full defense", not doing anything stupid, but not taking any actual action.
I use tokens on the table (in front of DM screen) to show initiative order. One for each player, and one for the monsters (more if I do individual init). This way, the players can see who's next, make the answer visible and obvious.
Making the answer visible and obvious is the same reason why I like battlemats. I wrote a blog about that, too. The gist is, you can see it for yourself, and save asking for clarification in most instances.
I instill a sense of urgency during combat, talking a bit faster, rushing, to get players to hurry up. This is how real combat is, and it gets people moving. Skipping slow players also encourages this.
I like Piratecat's suggestion on sitting in the middle, rather than the head. Though there is less room in the middle, it puts the GM at more equal distance from each player, which makes all players feel part of his game, rather than those closest. Definitely a psychological benefit.
On the point of giving suggestions to other players, I'd say that's a matter of preference and balance. Not everybody needs tips, not everybody takes suggestions well (though they need them), and not everybody gives advice well (often giving it as an order, not a suggestion). It can help, it can hinder. The real key, is to stop it when it's hurting, allow it when it's helping. Coordinated plans usually happen because somebody suggests an idea to somebody else (so they can build off it). Disallowing any talk outside of 6 words on your turn would pretty much hinder that.