The Kudzu is a climbing pea vine native to Japan.  Kudzu reproduce through nodes at it's roots which expand beneath the soil so that new plants can be pollinated and emerge away from the parent plant.  While this is the Kudzu's main method of reproduction, seeds are also produced.  However, these seeds may not germinate for several years, which can lead to the plant's reappearance after it had been removed.  This, combined with the plant being well-anchored into the soil, makes it difficult to completely eliminate the Kudzu from an area.

The Kudzu was introduced to the United States at the Japanese pavilion in the 1876 Centennial Exposition in Philadelphia and was first introduced to the Southeastern United States at the New Orleans Exposition in 1883.  The government initially planted millions of seedlings, believing the plant would help prevent ground erosion, and the plant was left unattended.  It thrived in the South's climate and environment and overtook native plants.

Today, the Kudzu has spread in the southern U.S. at the rate of 150,000 acres annually and is estimated to cover 3 million hectares in Alabama, Georgia, Florida, and Mississippi.

http://en.wikipedia.org/wiki/Kudzu_in_the_United_States

Once the world's most widely distributed mammal, the Gray Wolf now lives only in Canada and northern Europe, having been pushed out of the rest of North America (including most of the US), Africa, Western Europe, and the lower portion of Eastern Europe.  The gray wolf worldwide population numbered 2 million in the past; today, it is estimated at just 200,000 around the world.

Gray wolves have few natural predators, but human activities have reduced their populations to near-extinction in many areas.  Humans have severely infringed on the gray wolves' habitat and the habitats of their prey.  As previously stated, wolves once thrived throughout the United States, but hunting, trapping, and poisoning by humans has led to the severe decline of the wolves' numbers.  Hunting wolves is now illegal in some states (ie. Montana), but is not in many other areas.

http://en.wikipedia.org/wiki/Gray_wolf
http://earthjustice.org/features/campaigns/wolves-in-danger-timeline-milestones
http://www.defenders.org/wildlife_and_habitat/wildlife/wolf,_gray.php

Whitetail deers can be considered a keystone species (or named one's favorite keystone species) mainly because of their ability to live in a wide range of habitats.  Whitetail deers are typically thought to reside only in forest areas, however, they are found in a much wider region.  Whitetail deers live east of the Rocky Mountains in North America, Central America, and the topmost portion of South America.  In addition to the deciduous forest, they may live in savannas, open prairies, tropical and subtropical dry broadleaf forests, and wetland habitats.

This wide range of habitats allows the whitetail deer to support a wide range of communities.  They consume producers from each of these various habitats, and they are then eaten by different carnivores in each.  Thus, whitetail deers can help control plant life and support secondary consumers (carnivores) in a variety of regions.  Without the deer, producers may become overrun and carnivores may disappear. 

Whitetail deers may also be classified as an indicator species because it consumes only what it deems the best part of the plant, so if it is discovered that deer have moved on from an area, it may be because the plants in that area are diseased or there is some other similar problem within the plant community.

http://en.wikipedia.org/wiki/White-tailed_deer
http://texaslandconservancy.org/index.php?option=com_content&view=article&id=253:stew-brief

Poison Arrow frogs are extraordinary creatures whose main defense against predators are lipophilic alkaloid toxins secreted through their skin.  The most poisonous frog, the Golden Poison Dart frog, has enough venom to kill 10 grown men.  These toxins are lethal to most of the poison arrow frog's predators, and so, these animals avoid the frog.  Other frogs who share the same habitat as the poison arrow frog also learn to give the frog its space; the poison arrow frog is territorial and will fight frogs of the same and of other species.

The poison arrow frog's bright colors act as a warning to their predators that they are poisonous.  They may be blue, yellow, red, gold, or black, depending on the region they reside in. 

The poison arrow frog has the best adaptation in that its defense is so extreme, even species the poison frog would not harm still avoid the frog. 

http://www.honoluluzoo.org/poisonarrow_frog.htm
http://en.wikipedia.org/wiki/Poison_dart_frog
http://animals.nationalgeographic.com/animals/amphibians/poison-frog/