Some of the most useful permanent plants to grow for cooking are also decorative. If you have some space I highly recommend Citrus and in particular lemon trees.
Lemons - I grow 4 lemon trees as I use one or two lemons every day (sometimes more). There are two main varieties that are suitable for Australian conditions - Lisbon & Eureka, both have multiple crops and can be espaliered or kept pruned so you can reach the fruit. Lemons look striking as a feature espaliered on a masonry wall or fence. They are heavy feeders and need a high nitrogen fertiliser like chook manure applied a few times in the growing season, they like well drained soil with plenty of humus. Citrus trees like 20L of water per week in the growing season , and plenty of mulch around the root zone to keep the moisture in but do not mulch up to the trunk as this may cause collar rot. Citrus grow well in an open sunny spot away from strong winds and if you live in a cooler climate you may like to try growing citrus against a north or west facing sunny masonry wall. Lemons in pots are more for decoration rather than fruit production. I have used Emperor Mandarin in some of my landscape designs in the past as a hedge or screen - it looks stunning as it is evergreen, lush and can be pruned plus you get the fruit.
The Meyer lemon is not really a lemon but a cross between and orange and a lemon and are not as useful health wise or where lemons are called for in recipes as true lemons but still make lovely salad dressings.
Lemon helps to make your body alkaline even though they taste acidic they behave as an alkaline in your digestion. Lemons are very good for liver cleansing and contain vitamin C. I use lemons, limes, oranges and unpasturised apple cider vinegar that still contains the "mother" in my salad dressings - all other vinegars are acid forming.
Tahitian lime, mandarins and oranges, ruby grapefruit and blood oranges are also good to include in your salads, juices and smoothies. The zest of citrus skins adds a punch of flavour to many recipes.