Here is a really nifty little tip and trick to make interesting strokes by using the Appearance Palette in Adobe Illustrator. Start off by creating a 4pt stroke with the line tool, and make its color blue or cyan. Once this is done open the Appearance palette by clicking on its tab in the open palettes or if its not available go to Window > Appearance (Shift + F6) to bring it up.

With the stroke selected click on the little arrow on the right in the Appearance Palette and select Add New Stroke. Make this new stroke 3pt and a slightly lighter shade of the blue or cyan you chose initially. Keep adding strokes in this fashion until you get to 1pt stroke and you should have something like the sample here. When this is done you can save this as a style and easily apply it to any other strokes you want.