Pest

A line of ants — a line of ants going back and forth from their home to a food source

In addition to the welcome residents of a home, there are frequently pests - ants, cockroaches, rats, snakes, squirrels, raccoons, skunks, wasps, mosquitos, opossums and bats. Then there are the pests in the garden.

Repelling pests

Keeping pests out and discouraging their entry into your home is better than getting rid of pests or dealing with them once they are there.

Some tips:

store wood off the ground
seal holes into your home
store food in pest proof containers
some of the pests than like some garden plants don't like others -- suggestions
- plant basil near tomatoes (Some tomato pests don't like the basil, and the two make a wonderful cooking combination too.)
- marigolds repel some pests (including mosquitos, so gardening can be more comfortable)

Getting rid of pests

There are often services you can call to remove pests. Depending on the type of pest, you may wish to use an exterminator or a live, "humane" service. Here are some things you can do yourself.

Cockroaches

Boric acid is a useful way to get rid of cockroaches. They crawl through it and take it back to their nests where it kills them and their young. The other good thing about using boric acid is that it's not very toxic to humans and their pets. Sprinkle it on the counter ledges and edges of the floor where the cockroaches will crawl through it.

Rats and mice

snap traps, poison (careful of the safety of humans and pets in the home), ultrasonic waves and pest repellant (these last two are of controversial effectiveness)

Ants

There are multiple ways suggested to get rid of ants -- especially before they have established themselves. Try vinegar, black pepper, cayenne pepper, mint, bay or eucalyptus leaves or cinnamon. These things are not toxic for humans or pets, but some kinds of ants don't like them.

A mixture of borax and sugar is a popular suggestion. The sugar attracts the ants and the borax is taken home and eaten by the nest. Boric acid is also recommended in a similar manner.

Talcum powder, especially scented, and various other powders are also supposed to be ant repellants.

Mosquitos

Some plants that mosquitos are supposed to stay away from are (in order to be effective the scent must be released by crushing some leaves)

horsemint
rosemary
marigolds
ageratum (don't use on your skin)
mosquito plants (apparently more than one plant has this name)
catnip

References

Howto to rid your home of mice on WikiHowTo
the Frugal Life on [Getting Rid of Ants
Professional Wildlife Removal] for places in the US