High Defintion Camera (HD 1080P) Infrared Video Camera
Candles - supposedly, spirit activity can make the flame of a candle flicker in response. If you use this tool, do NOT leave the candle unattended.
Cell Phone - this is a theory that I am testing (the article will be posted soon) that cell phones cannot only give energy to the spirits but can also help them communicate. Celll phones pick up on radio waves so that we can communicate wtih one another so who is to say that spirits cannot also use it for the same reason. Some phones nowadays are equipped with a voice recorder. Although, I would suggest not keeping the digital recorder and cell phone next to each other during the investigation, just to ensure that there is no interference.
Talcum Powder - Good for indoor investigations, put some on a floor, table, etc and see if you can catsch any fingerprints or footprints.
Trigger Objects - examples: clothing, tobacco. Any object from a specific time period that can be used to trigger activity.
Wind chime - good for indoor investigations. Place in a room with no wind and see if you can get a response.
Besides the equipment for ghost hunting there are other items that are must haves for all paranormal investigators and hobbyists.
Cell Phone - I have this listed twice for a reason. Because even if you do not wish to use it for investigative purposes and even if you have walkie talkies to communicate with the other members in your group, a cell phone is necessary for all emergency purposes.
First Aid Kit - this is for a just in case situation. What you put in your kit is up to you. Useful items can include: bandaids, sanitizer, scissors, tweezers, 4x4 gauze pads and wraps to hold the gauze in place, a triangular bandage. In our group there are two people with CPR and First Aid certifications, which can also be a bonus to your group.
Flashlights - it is dangerous to wonder around in the dark without flashlights and/or night vision.