Yep lots of smoke & fire when clustering motors! When you see a motor for instance called D12-5 it's the same as a D12-3 the only difference is that when the motor reaches the end of it's burn , theres a 5 second delay before the parachute comes out rather than 3.
All the 24mm estes motors : D12-3 , D12-5 , D12-7 , D11-P , E9-4 , E9-6 , E9-8.
There are a wide range of 24mm motors available from Aerotech like others have said , and most of them are more powerfull than a normal Estes 24mm motor.
You should be able to get 'E' motors from any model shop that deals with Estes motors or Aerotech.
-Karl