Aquila Ukulele strings:

Aquila Ukulele strings pretty much changed the whole ukulele scene when they came on the market. The revolutionary nylgut material is truly remarkable in both tone and volume. As the name suggests, it's a cross between Nylon and gut.  Nylgut is a special nylon with similar properties to real gut, but without the issues of stretching or going out of tune in warmer temperatures that a real gut strings has.

Aquila make a huge range of ukulele strings, for soprano, concert, tenor and baritone. They offer a variety of tunings too, the traditional gCEA (High G); GCEA (Low G) for Soprano, Concert and Tenor Ukuleles; and DBGE for Baritone Ukuleles, and Tenor Ukuleles. Aquila also make a set specially for Banjo ukuleles.

Below is a choice of Aquila ukulele strings available from eBay: