I don't really see any reason why Bombs have to be limited to the "Charge and drop" model.
Remote Mines:
You don't charge at all, you click and a bomb is placed, but there is a small delay until the bomb can be exploded (very small). You blow the bomb by hitting your attack key again.
This self-balances the lack of charge time requirement. There is a "placement time" which prevents simply spamming it in the middle of the enemy, and you are restricted to a single bomb out at a time since the next attack you press will blow the bomb.
Charging this attack can allow multiple bombs to be placed at once, all of which will explode on the same following command.
Spider Mines:
These mines are placed as normal, but instead of exploding after a short time, they "get up" at that time and chase to the nearest enemy. In a sense, they are more "Homing Missiles" than Bombs at this point, but with a fairly short running range.
These ones are quite likely plain and simple BETTER than current Bombs. Since you can now act just like a normal bomber, minus the requirement to actually get in the middle of the enemy forces, since your bombs can walk themselves in. As such, they would need to do slightly less damage to compensate.
Proximity Mines:
These Bombs would have 2 radius indications. The outer one is the actual blast radius, and the (much smaller) inner one is the Trigger Radius. The bomb remains on the ground without exploding until an enemy crosses into the Trigger Radius, then it explodes and damages all enemies in the Blast Radius.
Again, flat out better than current bombs since you know that each one you drop will hit at least 1 enemy, as long as you are smart enough to bait/push them over there. You can also stack the bombs on top of each other to get a devastating effect. Possibly it would be required to set a limit to only 3 bombs active at a time (placing a 4th causes the oldest un-detonated bomb to evaporate)
Sticky Bombs:
These bombs would be thrown instead of placed. If they hit an enemy, then the bomb remains attached to that enemy until it explodes a short time later. If no enemy is hit before the bomb reaches the end of throwing range, it places on the ground like a normal bomb in that location.
Again, completely an improvement over normal bombs, unless your aim is horrible.
Gun puppy turrets! I know its not a bomb, but having the same deployment as a bomb would make a bit of sense. I love games with turrets and having the ability to deploy a gun puppy would be crazy fun.