These pendants make great gifts and are 3d printer friendly.
I have numerous letter combinations available for download at http://www.thingiverse.com/Ugly/designs
In your favorite 3d modeling tool create a 2 character text; your initials are a great start.
Text height 25 mm
Text only needs to be a curve (outline).
Note: Use a font that has the same height for each letter and not to curvy.
Step 2: Rotate
Rotate one of the letters 90 degrees to the other letter
Step 3: Align
Center the letters. Make sure that the bottoms are also aligned.
Step 4: Extrude
Extrude each letter separately the same width of the other letter.
Step 5: Intersection
Do a boolean intersection of the two extruded letters.
Step 6: Cylinder
Add a cylinder 3mm in diameter thru the center of the monogram.
Step 7: Boolean Difference
Subtract the cylinder from the monogram.
Step 8: Done
Upload to you 3d printer, print, and enjoy!