Nectar providing plants.
Not all plants produce nectar. Only the plants that use animals or insects as a way to fight off danger, or procreate produce nectar. Other plants use things like the wind. Some rely more heavily on nutrients from the ground, to pollinate and call for help if something starts to attack it. Nectar is a substance the plant produces to attract pollinators, or other protective animals. Some plants produce a nectar that is so specific, it only attracts a certain insect. Talk about putting all your eggs in one basket.
Generally, if it flowers, it probably produces nectar. Although, this is not always true. Some plants and flowers available from some of the bigger producers look good. The problem is, they are so hybridized that they do not actually produce nectar. They look pretty, but if they were added for a purpose, they will let you down. It is just something to keep in mind when purchasing plants for your property.
The importance of including nectar providing plants to the garden is to protect all of the plants. The animals and insects that are called in to help the nectar producing plants also help other plants. So, even if your focus in the garden is green things. Ensuring that you have some plants that produce nectar is important. Here are some options. More information will be added as time goes, so check back for more.