As mentioned above, dildos are amongst the earliest, and indeed the simplest kinds of sex toys. Dildos are also amongst the most pleasurable sex toys around, and have served humanity well for several thousand years already.
Shaped just like a large penis, and often just as desirable, modern dildos are usually made out of plastic or rubber, as these are the most comfortable materials. They are soft and do not cause harm to the genital area around which they are used. Dildos are primarily used to pleasure women, either by masturbating themselves or by having their sexual partner do this for them, although some men do enjoy using dildos anally, though this is quite rare outside of the gay community.
Dildos come in all shapes and sizes, from super-sized dildos to miniature dildos, double penetration dildos (which can be used to penetrate the anus and vagina simultaneously), and strap ons, which are often used by lesbian women to simulate intercourse with their partners.