Key players on the rig leading up to the blowout

The following people are reported to have been involved in the "skirmish" over drilling procedures which preceded the Deepwater Horizon explosion.

Robert Kaluza - BP "company man," well site leader.
According to The Atlantic, Kaluza said: "this is how it's going to be,"

Donald Vidrine - BP "company man," BP's top official on the rig.

Jimmy Harrell - Deepwater Horizon installation manager, a top employee of rig owner Transocean.
Harrell quotes before the fire according to The Atlantic-
Grumbling after the discussion: "I guess that's what we have those pincers for," referring to the blowout preventer on the sea floor that is supposed to be the last resort to prevent a leak in the event of an emergency.

Harrell quotes after the fire according to The Atlantic-
"Are you fucking happy? Are you fucking happy? The rig's on fire! I told you this was gonna happen."... "I am fucking calm,"... "You realize the rig is burning?"

In addition, the following people have issued statements-

Doug Brown - chief rig mechanic aboard the platform
According to the AP-

Doug Brown, chief rig mechanic aboard the platform, testified that the trouble began at a meeting hours before the blowout, with a "skirmish" between a BP official and rig workers who did not want to replace heavy drilling fluid in the well with saltwater.

The switch presumably would have allowed the company to remove the fluid and use it for another project, but the seawater would have provided less weight to counteract the surging pressure from the ocean depths.

Brown said the BP official, whom he identified only as the "company man," overruled the drillers, declaring, "This is how it's going to be." Brown said the top Transocean official on the rig grumbled, "Well, I guess that's what we have those pinchers for," which he took to be a reference to devices on the blowout preventer, the five-story piece of equipment that can slam a well shut in an emergency.

Truitt Crawford - Transocean rig worker
According to the AP-

In a handwritten statement to the Coast Guard obtained by the AP, Transocean rig worker Truitt Crawford said: "I overheard upper management talking saying that BP was taking shortcuts by displacing the well with saltwater instead of mud without sealing the well with cement plugs, this is why it blew out."

Mike Williams - Transocean's chief electronics technician
According to The Atlantic-

Transocean's chief electronics technician, Mike Williams, also recalled the argument but named a different BP "company man," BP's top official on the rig, Donald Vidrine.

Sources-
Heated Argument on Rig Before Blast « Colonel6's Blog
'The Rig's on Fire! I Told You This Was Gonna Happen!' - National - The Atlantic
Oil Rig Official Says He Tried to Activate Emergency System - NYTimes.com
Oil Rig Official Says He Tried to Activate Emergency System - NYTimes.com
AP Exclusive: Workers describe failures on oil rig
Top BP official on oil rig takes the fifth; another says too sick to testify | Raw Story
Half of the dueling duo will be absent in Coast Guard hearings today *Update* | NewsWatch: Energy | Chron.com - Houston Chronicle