The concept of a vampire, while widely known, varies greatly in actual detail. Most of us know it as the sharp-fanged undead, rising from its coffin to drink the blood of the innocent by night and taking refuge from sunlight there by day. Vampires are said to be repulsed by a cross, vulnerable to sunlight, killed by a stake through a heart and unable to cross running water. However, like most myths, there are many variations on this basic theme.
Bram Stoker's original vampire legend, written in 1897 and perhaps the best known before modern interpretations such as Buffy and Interview With the Vampire. Dracula defined the vampire as we know it. Like Grandpa in The Munsters, the vampire wears dramatic capes, looks perfectly human apart from a little pale skin and pointed teeth, lives in Transylvania and dislikes the regular vampire things. Dracula was originally inspired by Vlad Tepes, perhaps known better as Vlad the Impaler, who it's estimated had around 100,000 people killed during his lifetime by impaling them vertically on spikes and letting gravity do the rest.
Buffy the Vampire Slayer
The vampires in BTVS are somewhat different from many other interpretations of the creature. Staking a vampire through the heart conveniently turns it to dust, ensuring that the police never find any bodies - this is different to most other vampire myths, where removing the wooden stake from a vampire's heart allows it to return to life. This form of vampire can choose to look entirely human, but their facial features take on a monstrous, feral appearance when they move in for the kill. They are always supernaturally strong, and excel at unarmed combat. As usual, "Buffy" vampires cower in fear at the sight of a crucifix and are burned by holy water and sunlight which they avoid at all costs, and cannot enter any building uninvited. (One vampire in the series finds a clever loophole in this limitation, by entering a high school whose latin motto translates to "Enter here all ye who seek knowledge".) Decapitation is as effective against them as a stake, which makes for some fun swordfight scenes. To the best of my knowledge, they are not harmed in the slightest by normal water, and have no real aversion to garlic.
Interview With the Vampire
A rather excellent horror movie starring Tom Cruise, Brad Pitt and a young Kirsten Dunst as vampires. The vampire society as portrayed in the film is the well-known old-style finery and decadence that comes from a society where the nostalgia goes back centuries. In this interpretation, vampires must feed on the blood of living humans to survive, and their victims rise again as a vampire. Along with their eternal youth and beauty, injuries taken begin heal immediately to restore the vampire to the form they had when they became a vampire - much to the dismay of Kirsten Dunst's character, who finds that she is stuck in the body of a child and even unable to chage her hairstyle. At one stage in the movie, a vampire is trapped in a coffin which is bricked into a wall for centuries as a punishment, his vampiric immortality leaving him trapped, alone and conscious for centuries without the ability to satisfy his craving for blood.
Legacy of Kain (Soul Reaver)
A rather excellent game, starring a revenant ex-vampire as the protagonist and an eerie array of regular vampires as the majority of enemies. In the game's opening FMV, the vampires (the protagonist included) are a society of slightly monstrous-looking humanoids (no mistaking them for humans), but at the start of the game proper they appear most definitely as nonhuman monsters with the boss characters as various massive abominations. The vampires can be injured in a fight, but their wounds immediately begin to heal (similar to Interview with the Vampire) and a creature temporarily incapacitated in this manner must be finished off in some other manner by exploiting one of their vampiric weaknesses. Standard methods include impaling through the heart (Raziel is an uncannily good shot with a pointy stick), destroying the body by fire, immersing the creature in water or exposure to hard-to-find sunlight. Some vampires have found themselves with an immunity to one or more of these elements. Exploding your foes with (Garlic and crosses don't feature in this game.)
Dungeons and Dragons
Way at the back of the Monster Manual, the Vampire is treated a template which can be applied to any humanoid creature. A vampire can be created in one of two ways, the first of which is when a creature is killed by an existing vampire's Blood Drain ability, the second is when an evil cleric of at least eighteenth level casts Create Greater Undead on a body. The base creature takes on the undead type, becomes tougher, stronger and more powerful, and gains a veritable host of special abilities. Natural armor increases by +6, the vampire gains a Domination (mind control) ability, his touch deals two negative levels to a living foe, he can bite and drain all of a creature's blood and summon a horde of bats, rats or wolves once per day, the vampire gains damage reduction 15/+1 and cold and electricity resistance 20, fast healing 5, can assume gaseous form or the form of a wolf or bat will, can walk normally on walls and ceilings and gains Str +6, Dex +2, Int +2, Wis +2 and Cha +4. They gain the feats Alertness, Combat Reflexes, Dodge, Improved Initiative and Lightning Reflexes, and gain a +8 racial bonus to a whole host of skills. However, they have all of the standard vampiric weaknesses, despite their power. They cannot cross running water and cannot survive immersion in it, note can they tolerate garlic and are repulsed by the sight of a mirror or holy symbol. They may not enter private property unless invited, and spending any more than a few seconds in direct sunlight destroys them instantly. Staking a D&D vampire's heart effectively kills it, but the vampire can simply get back up if the stake is removed, as long as its body remains intact. Vampires are always chaotic evil. Although becoming a vampire is a boon for most evil creatures and characters, a particularly mean DM may apply the vampire's estimated ECL +10, requiring a 5th level character to earn 16,000XP to increase one level instead of only 6,000XP.
I'm not even going into this one.
(Sources: The Giant Book of the Supernatural by Colin Wilson, ISBN 1-86487-372-5