in HL2, there's an unused exlosive known as the SLAM. (it's in HL2DM, though)
It's a nice weapon, so let me describe it.
You can throw it with MOUSE1.
After this, hit MOUSE2 to detonate it, or throw some more.
If close to a wall (literally touching), you can plant it to the wall. after a short arming time, it lets out a laser that can go over an infinite distance. anyone who trips this laser makes it explode, so be careful about your positioning, or some random sniper will trip it. You can also plant it to the floor (you need to crouch) to use it as a landmine. The wallmounted SLAMs don't detonate with mouse2, but you can shoot them if you need to.
Now, i'm not sure how most of these mechanics can translate to BL. modify if needed, just throwing the idea out there.