Nurikabe

Rules: Colour some unclued cells black so that the remaining cells form several polyomino-shaped islands. A clue equals the area of the island that contains it; each island must contain exactly one clue and different islands must not touch by side. All black cells must form a single polyomino that does not contain a 2 by 2 square.

Example:

nk-0

[Solution]

Here is the Wikipedia article.