draw an oval and use the erase tool to remove the parts you don't want.
Use the bezier pen tool, then convert to movie clip
Variety is the spice of life... another approach...
Draw a rectangle and fill it with a radial gradient. Draw a diagonal line thru the rectangle that intersects the rectangle's line at the same locations as that curved line appears to intersect. With nothing select, put the mouse on the right middle of that diagonal, press down and drag the line to a curved shape that matches the curve you want. Select and delete the lines and fill you don't want... below is a quick rendition, though not attempted/intended to be an exact match...
Also, if you just want to draw a curved line, draw a straight one and just bend it as described above
Ha, wow! Thanks for all the awesome ideas guys; they all worked great.