General:
* Shocking
* Outrageous
* Disgraceful
* Immoral
* Reprehensible
* Offensive
* Indecent
* Unseemly
* Improper
* Objectionable
More Intense:
* Infamous
* Notorious
* Tabloid
* Sensational
* Sordid
* Vile
* Depraved
More Subtle:
* Questionable
* Unconventional
* Controversial
* Unsavory
* Disreputable
Focusing on gossip and rumors:
* Rumor-mongering
* Gossip-worthy
* Sensationalized
Focusing on the nature of the scandal:
* Immoral
* Dishonorable
* Corrupt
* Deceitful
* Treacherous
The best synonym for "scandalous" depends on the specific situation and the level of intensity you want to express.