I accidentally stumbled on a handy little trick for summoner builds who have to summon hordes of things but are annoyed by huge mana costs.
1. In town, find the person who automatically refills yours mana bulb. (Orimus in act 3 etc.)
2. Left click on him/her to bring up their options menu, leaving it up.
3. Push the Hotkey of your desired summon skill so that it is selected right side skill slot.
4. Spam right click to summon all of your minions quickly without running out of mana.
5. Profit.
What happens is everytime you right click, it will summon a minion and instantly refill your mana bulb at the same time, leaving the townsperson selected. This way you can summon all of your 15-30 (whatever) minions in a few seconds, regardless of the mana burden.
This might not be new to anyone but me, (I have no idea) but I like to share happy accidents. I hope this helps someone.