Pirahã: no grammatical recursion and much more; whistled languages
Pirahã is quite a remarkable language
* no grammatical recursion
* one of the smallest known phonological system: between 10 and 13 phonemes
* the simplest known kinship system (the only family words are "parent" and "sibling")
* 3 numbers: "a few", "some", and "many", and an inability to distinguish 4 from 5, and apparent inability to learn numeracy skills.
* it can be whistled, hummed, or encoded in music
* it has grammatical "evidentiality" (indicates whether the speaker saw the event happening), which English lacks.
* their culture has no history beyond living memory

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

As the expressivity of whistled speech is limited compared to spoken speech, whistled messages typically consist of stereotyped or otherwise standardized or set expressions, are elaborately descriptive, and often have to be repeated. However, in languages which are heavily tonal, and therefore convey much of their information through pitch even when spoken, such as Mazatec and Yoruba, extensive conversations may be whistled.