Breeds that are Similar to Siamese Cats

Balinese - long haired Siamese.
Burmese - Descendants of a cat found in Burma named Wong Mau in 1930. Wong Mau was bred with a Siamese, and while Burmese aren't technically derived from Siamese, they were initially thought to be a variant of Siamese, hence crossbreeding.
Colorpoint Shorthair - The result of crossbreeding with other shorthair cats. Resembles a Siamese except for the lack of traditional coloring.

Himalayan - Derived from crossing Persians with Siamese. Referred as a Colorpoint Persian in Europe, and considered to be a member of the Persian breed by CFA.
Javanese - Longhaired version of the Colorpoint Shorthair.
Ocicat - Result of crossing an Abyssian with a Siamese; a spotted cat.
Oriental Shorthair, Oriental Longhair - Same style as a Siamese, with non-pointed colors, including tabby, silver, and tortoiseshell.
Tonkinese - Cross of a Siamese and Burmese. Tonkinese have the typical points, but their bodies are traditionally darker.