What can I do if I had been renting a house and the landlord repeatedly ignored requests for maintenance and repairs to be made?

If you are still there and you have provided your landlord with written notice of repairs affecting habitability and he still, after a reasonable time to fix them, has not addressed the issues, you could withhold your rent; if/when he tries to evict you, you would raise the impairment of habitability as a defense, and if the court finds that your use/habitability of the premises was impaired, it may order the landlord to make repairs and/or order that you be given a rent abatement (credit) for the time you lived with impaired conditions.

Note that only conditions which would make the premises uninhabitable matter--the landlord is under no duty to freshen paint, repair a dripping sink, tighten loose cabinets, patch holes in walls that do not let in drafts from outside or destroy privacy, etc., and there is no compensation for such relatively minor issues. He does have to fix leaks that can cause mold, holes in doors, walls windows letting in drafts, nonworking stoves, nonflushing or  oveflowing toilets, etc.

Alternately, you may be able to use the landlord's violations of the "implied warranty of habitability" and also the "covenant of quiet enjoyment" (if he repeatedly entered without notice when it was not an emergency, depriving you of the undisturbed use of your premises) as grounds to treat the lease as terminated and move out. Be careful though, because if you have a written lease and the landord sues you for rent due under it, if a judge disagrees and feels that the problems were not so significant as to warrant terminating the lease, you could find yourself still liable for the rent due under the lease.

If you have already moved out, you may be able to sue the landlord to recover compenation for the time period you lived with impaired habitability and/or landlord harassment (entering without notice) and get some amount of rent credit back.