Culled From http://www.fcc.state.fl.us/fcc/reports/monitor/methmon.html and other related websites
After being cleared by the Governor and Attorney General, a sedative is offered and the condemned is led to the execution chamber where he is secured to a gurney by his legs, stomach, chest, biceps, and wrists. Intravenous tubes are inserted into both arms (One primary, one backup) and a saline drip is started.
After the warden asks for a last statement, the prisoner is administered a lethal dose of Sodium Pentathol to render unconsciousness. After the first injection, the lines are again cleared with saline to avoid any possible chemical reactions that may cause clogging. Following unconsciousness, the prisoner is administered a dose of Pancuronium Bromide, which causes muscle relaxation and the collapse of the diaphragm and lungs. After another saline flush, the condemned is finally administered potassium chloride to stop the prisoner's heart. In its entirety, the average execution takes around 17 minutes, about 2 of which actually involve chemical administration.
Some reports I have read suggest that an Anal Plug and Catheter are used to avoid any "messy cleanup", but this either isn't standard procedure, or isn't mentioned elsewhere.
Also, different states appear to use different chemicals to induce the initial unconsciousness.