I'm doing a review of an instance that has been running for a couple of years now.
Is there a way of getting a list of all the current trigger campaigns running in an instance?
Click the Marketing activities root folder, then "campaign inspector". You will be able to filter only the active triggered campaigns.
You need to enable the Campaign Inspector in the Treasure Chest:
Then click back in Marketing Activities and click the Campaign Inspector tab:
Some more information here: Release Notes: December 2012 - Marketo Docs - Product Docs
In Marketing Activities, you can filter on all triggered campaigns using the filter icon to the right of the search bar. (see image below)
I hope this is what you were looking for.