it's really the only species that I hate with a passion, and since they don't really serve any ecological role (they don't eat other organisms, just leech off them), they're would be no consequences
An organism doesn't have to be a predator to have an impact on the food-chain.
If the organism is itself eaten by other creatures, then it disappearing may have an affect on that predators population, and in turn have a knock-on effect on any other predators/prey of the declining population.
There are several species which consume mosquitos, either as a small part of their normal diet, or as a large part.
Bats are known to eat mosquitos, but so are several bird species (purple martins, swallows and waterfowl), as well as fish (goldfish, guppies, catfish, and notably the mosquito fish all prey on mosquito larvae), and insects (such as dragonflies and damselflies).
Mosquitos also pollinate flowers. Only female mosquitos feed on blood, so for the adult males the majority of their diet comes from nectar from flowers, and in gathering it they pollinate them.