According to a 2006 article by Losey and Vaughan, the services wild insects freely provide are worth at least 57 billion dollars annually.
These estimates are based on the services insects provide in:
1) Dung Burial: 0.38 billion/year
Several “dung beetles” from the superfamily Scarabaeoidea make a valuable resource out of our waste.
Picture from: http://simple.wikipedia.org/wiki/Dung_beetle
2) Pollination: $3.07 billion/year
Not only managed bees such as Apis mellifera (the western honey bees) pollinate important crops but wild bees also pollinate wild and domesticated flowers, helping to provide us with blueberries and apples.
Normia melanderi (the Alkali) visiting alfalfa
According to the USGS, native bees are estimated to pollinate up to 80% of the flowering plants in the world (http://www.usgs.gov/blogs/features/usgs_top_story/the-buzz-on-native-bees/)
Bumble bees (Bombus) are effective at pollinating tomato flowers, like the one pictured below.
3) Pest control: 4.49 billion/year
Insects also defend our gardens and farms from pests that, if unchecked, could munch our crops away.
A ladybug (Coccinillidae) feasting on an aphid, an insect that sucks the sap out of a wide variety of plants.
Alligator weed flea beetles (Agasicles hygrophila) keeping alligator weed, an invasive weed in most southern states of the USA, at bay.
4) Recreation: $49.96 billion/year
Hunting small mammals, bird-watching, and fishing are all popular hobbies. Many of these animals that are the object of these hobbies depend on insects for food. If insect populations, these birds, small mammals, and fish would most likely suffer along with them.
A trout preparing to swallow down a mayfly treat.
A favorite bird for bird-watchers the charismatic scarlet tanager (Piranga olivacea) is clutching a meal. They are primarily insectivores.
Not only are insects awesome in and of themselves, it is clear they have clear monetary value that many do not think of when looking at them crawling or flying about.