Per a little forum post here are the available deinterlacers for mencoder.

-vf lavcdeint -vf kerndeint -vf filmdint -vf pp=lb -vf pp=li -vf pp=ci -vf pp=md -vf pp=fd
I've had good luck when using them with scale, as long as you scale after the deinterlace.

-vf pp=ci,scale=640:480