A good forum is this:
http://forum.ukuleleunderground.com/
They also have a marketplace to buy/sell Ukes.
Some videos:
http://ukuleleunderground.com/video-library/
Also it depends what size you like:
I copied the below from
http://www.ukuleleworld.com:
SOPRANO UKULELE - The Soprano (often called "standard" in Hawaii) is the smallest, and the original size 'ukulele. Most beginners start with soprano ukuleles because they look and sound cute.... yet, the soprano ukulele is a fine musical instrument, easy to learn, easy to play, and fun!
Personally I find them too small!
CONCERT UKULELE - In the 1920's the Concert size was developed, and designed to be an enhanced Soprano, being slightly larger and thus slightly louder and deeper sounding tone even when tuned to the same note. Many people with larger hands prefer the concert ukulelle. The one I have is concert size.
TENOR UKULELE - And a few years later the Tenor was created, being much larger than both the Soprano and Concert, and thus more volume and deeper bass tone. The Tenor size often has one or two wound bass strings, producing even more deep resonance. Many professional musicians play tenor ukuleles as these instrument's sound is louder and bolder.
BARITONE UKULELE - The largest size 'ukulele is the Baritone. With a 10" body width, and tuned DGBE (the same as a guitar), it is considered a miniature 4-string guitar..... like the 4-string Parlor Guitar, only smaller in size.
I bought my one (a Kanile'a) in Concert size from Ken in Hawaii, he gives some ideas here:
http://www.youtube.com/watch?v=fASgb8m2GUc
Some brand names that come to mind: Kala, Mahalo, Lanikai, Pono, Kamaka. Most of the lower end ukes of all manufacturers are made in Asia and mostly laminated wood.
Here's a video where a German guy compared 12 of them. Don't listen to the first 2:50, jump immediately to minute 2:50:
http://youtu.be/sl65bQ3sn-g
Here's one comparing 10 others:
http://youtu.be/TBmEHVcZvB8
Ralf