where are all the filters hiding????

I used to be able to print_r( get_defined_vars() ) within my theme and somewhere within all that mess lived an array of defined filters / actions. I cannot seem to find it anymore I’ve also tried print_r( $wp_filters ) and print_r( $merged_filters ) with no luck. My goal here is to create a <select> input where all of it’s options are the names of valid filters — just need to know how to get the list. Thanks in advance!!!!