What do you want the knife to do? An inexpensive classic Buck lockback will handle a surprising amount of abuse and is easily improved by a little work on the blade profile (and they are heavy and they will "jump lock" regularly when pounding on it to split wood - which is managable - I still have all my fingers at last count... 1, 2,3, ... 8..). A SAK locking knife with a saw etc will do other things well (I have never split any serious billets with one and would rather not) Axis locks are highly regarded - knife forum guys have a lot of discussion on them.

Doug mades some suggestions here but I don't own many of those so cannot comment on them.