I have had moderate success with my tomatoes this year. I think the long hot dry we are having in Northland has taken its toll. I still have a few plants with fruit on but have pulled out about half so far as they have died off. This is about a month or more earlier than usual. I planted basil and marigolds around all of my tomatoes. Have not had any pests or diseases at all. I also had one tomato growing beside a parsley plant. However very hard to tell if these companion plants do actually make a difference. I would love to see some research into this.
Interesting. I've been researching this and have come across a number of references that say NOT to plant tomatoes near brassicas, ruling out brussels, broccoli etc as companions (see for instance, http://www.gb0063551.pwp.blueyonder.co.uk/seeog/companion/ ). Also not near potatoes, corn or beans. I'm interested in people's observed experiences in NZ gardens though, there may be significant differences between what works in North America and Europe and here.