#96 - Escher inspired interlocking keys looks pretty cool.
http://www.annexed.net/images/escher/escher1.jpg#90 has the key hole. Maybe these two can be combined. Make the keyhole in the U match color of the primary key (only one of the color), and the U match the color of the other letters.
coloring - i think these colors clash the future nexul.com theme colors (per the attached screenshot). Use the blue/green or blue/orange combinations mentioned in the brief.