The Latin:
VRSNSMV: Vade retro, Satanas. Numquam suade mihi uanas.
The English:
Begone, Satan. Do not tempt me with vanities.

[For more on the famous cross-medal, visit the Benedictine Home. The picture is from there, too.]
The Latin:
Eius in obitu nostra praesentia muniamur.
The English:
May his presence strengthen us in the hour of our death.
[For more on St. Benedict's cross-medal, visit the official site.]
The Latin:
NDSMD: Non draco sit mihi dux.
The English:
May the dragon (devil) be not to me a guide.
[For more on the jubilee cross-medal of St. Benedict, visit the official site.]
The Latin:
CSSML: Crux sacra sit mihi lux.
The English:
May the Holy Cross be to me a light.
[For more on the jubilee cross-medal of St. Benedict, visit the official Benedictine website]