These are a few uke accessories I have enjoyed in my tenure as a ukalalien:
The Ukalalien Songbook by Kate Power and Steve Einhorn, replete with CD, fun artwork, and chord charts:
I also recommend getting a ukulele with pegs or ordering pegs to put on your uke and adding a shoulder strap. You can play your uke with more ease and then sling it behind your back and walk around looking cool!
You can find some great, handmade uke straps on Etsy:
I designed a fun one from Island Provisions: