Lightning Deadlifts are one of my favorite drills to build explosive bar speed off the floor. It combines accommodating resistance (i.e. the weight gets heavier toward lockout) and post-activation potentiation (i.e. the second rep is lighter so you can lift faster), so it utilizes two excellent means of improving bar speed.
If you’ve got chains and some buddies, try out Lightning Deadlifts. I especially love using them in a team setting so lifters can help and encourage each other. Check it out: