None. I'm Old School™.

Pretty much exactly as caitlinsdad said. It starts with a steady hand and good pens (I like Sakura Microns), then following up with appropriate contrast adjustment to the scan to solidify the blacks and remove the paper grain or tint.

I find that when you scan in black and white drawings, you can increase the brightness and contrast settings to get rid of paper grain/erasure marks. Make sure your software is scanning as a black and white and not a greyscale or color picture. I think there is a function to smooth out jaggies to convert images from bitmap to vector/raster images. I am old school too and don't have a digitizing tablet to draw on yet, I prefer to do things freehand.

pburgess' lettering is pretty good and consistent. I use pencil guidelines and try to imitate a style or font for cartoons. You can try various type pens or markers with different shaped chisel or round tips to get those varying line thicknesses in the letters. Calligraphy is fun to try to do.

Look at forums member signature post to check out what some people did to clean up scans of doodle/signatures.