I had 4 convict cichlids in my tank.. purchased at the same time all the same size.... well i have one left.. that one killed off all the others...

What fish can I put in with this one.. its a 35 gallon tank with plenty of hiding places...

Well usually plecos do ok, but some times even they get picked on when they are the only fish to pick on.
How big is your convict? I have a convict in with a pair of Jack Dempseys. The Dempseys only bother it when they have fry. Other then that all 3 fish just hang out in a hole under some drift wood.
Note the Dempseys are about twice the size of the convict at the moment.

yep the pleco fell victim last ... the convict is about 4 inches now. all the fish i see in the fish store are smaller than it is .... i am wondering if i just get as big as i can and get a small number of them maybe they will make it to get big enough to not let it pick on them ?