For shadow, Affdotspriest and Gnosis are essential. A good nameplate setup is also crucial, and while many use tidyplates, I find Elv's nameplates are great as well. Also, a configurable boss unit frame UI so that you can track your dots on multiple boss frames. And another chime for weakauras, which is essential for anybody playing WoW these days.
For healing, Grid+clique (browse grid modules to get it nicely setup) and ofc weakauras get the job done very well.