From the lowest to the highest string (4th, 3rd, 2nd, 1st):

Soprano:
A D F# B or G C E A
Concert:
A D F# B or G C E A
Tenor:
G C E A
Baryton:
D G B E

Note that on the Soprano and Concert instruments, the lower string (or fourth string) is pitched a 5th higher than the third string.

You can download a ukulele tuner here: http://www.ukulelist.com/download-ukulele-music-software.php