Nicotiana and artemisia act as general repellants - neither insects nor animals like their pungent scents. Many aromatic herbs such as rosemary, garlic, mint, parsley and sage, tend to repel certain insects and, thus, make good companions. The pollen and nectar provided by these plants attracts natural insect enemies. However, keep in mind many on the list are also very attractive hosts to butterfly larvae. This can be a blessing if you enjoy butterflies, but the larvae will feed on the foliage of these plants.
Some plants are contrary companions.
Other plants are plain disagreeable. Intermingle your plantings with a variety of species to achieve not only a healthier garden but also a more unique, diverse and altogether enjoyable gardening experience.