From the Wikipedia category list [1]
- Alekanovo inscription
- Ancient inscriptions in Somalia
- Butuan Silver Paleograph
- Cascajal Block
- Dispilio Tablet
- Gradeshnitsa tablets
- Ikom monoliths
- Käymäjärvi Inscriptions
- La Mojarra Stela 1
- McClelland Sherd
- Ndakunimba Stones
- Newton Stone
- Olmec hieroglyphs
- Phaistos Disc
- Phaistos Disc decipherment claims
- Rongorongo
- Singapore Stone
- Sitovo inscription
- The Starving of Saqqara
- Tărtăria tablets
- Tuxtla Statuette
- Youra Potsherds
- Zapotec writing
See also Undeciphered writing systems and Inscriptions of disputed origins
There are many websites of varying degrees of credibility covering these topics.