General synonyms:
* Tiny
* Small
* Petite
* Diminutive
* Little
* Wee
* Microscopic
* Pocket-sized
* Compact
* Reduced
Synonyms emphasizing scale or size:
* Scale model
* Reduced-scale
* Downsized
* Shrunken
Synonyms for "miniature" used in specific contexts:
* Painting: Thumbnail, sketch
* Artwork: Miniature portrait, cameo
* Book: Pocket edition, abridged
The best synonym depends on the specific meaning and context you want to convey.