A brief summary of some Workflow enhancements plugins.
The main focusing is primarily on what they contribute on the Post-Function side of a Transition.
Workflow Enhancer for JIRA
Marketplace: https://marketplace.atlassian.com/plugins/com.tng.jira.plugins.workflowenhancer
Interesting, but not that exiting Workflow plugin - but its free 
It has one unique facility - the ability to fire a Post-Function after evaluating a boolean - this can be used for "condition" avaluation, here shown in pseudo code:
If {Text} == "A" Fire: Update Resoulution Field to "A"
If {Text} != "A" Fire: Update Resoulution Field to "B"
Several part of the Post-Functions "Create" or "Add Comment" - I never got them working
JIRA Misc Workflow Extensions
Marketplace: https://marketplace.atlassian.com/plugins/com.innovalog.jmwe.jira-misc-workflow-extensions
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An interesting but not free plugin, one of the very good points being that several post-functions has "Conditional execution of post-functions" - wich as the above description enables some conditional execution of the fuction.
Number 8 and 9 is quite existing and worth examining further.
JIRA Suite Utilities
Marketplace:
One of my (free) favorites,
JIRA Workflow Toolbox
Marketplace: https://marketplace.atlassian.com/plugins/com.fca.jira.plugins.workflowToolbox.workflow-toolbox/versions#b400
This has some very good field post-fuctions for handling lists and formatting text fields.