Depends on how much control you want. There are easy ones like AutoGK that give a reasonably good result and there are easy, but clunky ones like SUPER that read a lot of input formats, but is kinda limited wrt. output settings.
Then you have mencoder and the Windows GUI megui which will give you an insane amount of freedom.
For audio, you have the converter in Foobar2000 which lets you batch-convert things and you have the special purpose stuff like OggdropXPd and LAMEdropXPd which will let you drag and drop a wav and it will encode it for you.