Males of all members of the cat family have backward-facing spines on the penis, which cause pain to the female when he withdraws from her. This helps to stimulate ovulation in the female - female cats are induced ovulators, which means they require the stimulus of mating before their bodies release eggs. Female felids often turn on their mates when they withdraw, snarling and clawing, because of the pain the spines cause them.
Tigers are the largest of all cats, with the Siberian (or Amur) subspecies being the largest. However, the largest cats which ever lived were the European cave lion and the American lion, both of which were around 25% larger than modern lions - they stood around 5 feet tall!
Lions are the only truly social cats, living in large family groups called prides. The male lion is the only cat which has a mane - this makes him appear larger and more intimidating to other males, more attractive to females, and helps protect his throat during fights.
Cheetahs are the fastest-running animals in the world, reaching speeds of over 70mph for short distances. They are the only cats whose claws are only partially retractile (other cats have fully retractile claws), which helps them grip the ground when running.
The smallest cats in the world are the black-footed cat and rusty spotted cat, both of which are only about half the size of a domestic cat.
The only cats which are capable of roaring are those of the genus Panthera, the tiger, lion, jaguar and leopard. Part of the hyoid apparatus in their throats is made of cartilage rather than bone, which allows them to roar. They are sometimes described as 'the roaring cats' for this reason.
The clouded leopard has the largest canine teeth of any living cat in comparison to its size. Here is an image of its skull:
http://www.skullsunlimited.com/graphics/…
The extinct sabre-toothed cat Smilodon had upper canine teeth up to 8 inches long.
Lions and tigers can interbreed and produce ligers (offspring of a male lion and female tiger) and tigons (offspring of a male tiger and female lion). These hybrids are usually sterile, but occasionally a female will be fertile. Other hybrids include leopons (leopard-lion hybrid), pumapards (puma-leopard hybrid), and puma-ocelot hybrids.
Melanistic leopards - that is, leopards with an excess of the dark pigment melanin, resulting in an almost totally black coat - are often referred to as panthers. Some people do not realize that a panther is simply a black leopard, and think it is a species in its own right.
White tigers with black or brown stripes and blue eyes are often mistaken for albinos. Albinism is a complete lack of pigment, meaning an albino tiger would have no stripes and pink eyes. The condition these tigers have is actually leucism, a genetic condition which results in reduced pigmentation. This is only known to occur in Bengal tigers. Leucism also occurs in lions - in the wild this condition is only known to occur in the Timbavati region of South Africa.
EDIT: In response to alphanot's answer, I must point out that 'a male wild cat will not share his territory with another wild cat' is not strictly true. A male wild cat's territory will often overlap the territories of several females. In the case of lions, a pride can have between one and eight adult males (two to four is most common), who are often but not always related, and up to 30 females, who are always related to each other, but not to the males. Male cheetahs from the same litter will also stay together for life.

