General synonyms:
* Wealthy
* Prosperous
* Rich
* Opulent
* Well-off
* Affluent (yes, it's its own synonym!)
More formal synonyms:
* Moneyed
* Substantial
* Prosperous
Synonyms emphasizing specific aspects:
* Luxurious (emphasizes material wealth and comfort)
* Comfortable (emphasizes financial security)
* Successful (emphasizes achievement and accomplishment)
The best synonym to use will depend on the specific context and the desired level of formality.