This is a weird issue because a decent portion of people report that every fight in 4e takes them two-plus hours to wrap up even after it's clear who won, while another decent portion of people report that combats are always fast and furious and finish nicely for them, while yet another decent portion of people report that combat is usually fast and and furious except when it's against a solo monster, which is when it turns into a two-plus hour mop-up.
Me, I'm firmly in the "Every fight is so frickin long" camp. I have fixed this by having everybody do automatic maximum damage without rolling for it (and double on crits). For our group, this has turned combat into a fast, furious, dangerous and strategic thing where a wipe is always around the corner if you're not paying attention, while still not being or feeling broken in any way. I recommend it if your players get excited over the idea of actual dangerous combat (I think we can generally agree that regular 4e combat isn't actually that dangerous for the players, although some people won't of course) and take the idea of a possible wipe as a personal challenge to beat.
At first my players were hesitant about the idea of not rolling for damage ("It makes me a little sad," one of them said), but after I convinced them to try it for one session, the combats' speed and general feel improved SO MUCH that we immediately adopted them.
This also has the effect of turning level-3 and level-4 monsters into "improved minions" right off, one hit to bloody, another hit to kill. I think the improved minion idea is fantastic though, if you're not doing max damage then I recommend doing that for sure.