The combination of basil and tomatoes is considered by many to be the height of complimentary tastes. Used extensively in Italian cooking it is included in sauces, pizzas and tomato salads.
This is a good time to sow basil (May - June) to add to all those tomato based dishes that are so popular over the summer months and basil is easy to grow when the weather is warm.
The other herb that goes well with tomatoes is coriander. Often used as a garnish for spicy dishes, especially curries, its seeds are also crushed and made into sauces along with other spices such as cumin.
The garnish of cherry tomatoes and coriander leaves on curry dishes is a culinary luxury that to me rivals the the great taste of basil and tomatoes. Coriander is also easy to grow as is cilantro, a variety of coriander.