Looking for a one piece ultra light/light rod under $100 in the 5'6"-6'.  I read a lot about light tackle/small baits and the success and enjoyment of it and tried it this past summer and had some fun with it using a $25 ultralight spinning combo.  I think I want to upgrade with a better rod and match it up with a 500/1000 size reel.  Any suggestions?

Older model Daiwa procyon with the Fuji components from fleabay would be my pick. I have mine paired with a Sahara 1000 and it's a blast to fish. 

I have a St Croix Premier 6' UL rod. I like it as well as my other Premier rods, except that it is rated fast but has almost a slow action. Super whippy. It can be good or bad depending what you're fishing for.

I used to use the 6' Quantum Tenton Trout rod. Not overly expensive, but it was a nice little rod. It got me through my college years living close to a lake with a stunted bass population. It was very whippy, but I'd fish 4" rubber worms on it and managed to hook plenty of fish. 

I've caught a bunch of trout on my Shimano Sojourn UL rods (4'6" 1-piece and 5'0" 2-piece) and they only run $30-35.  It looks like the 1-piece is discontinued but they still make the 2 piece.

B n' M offers a nice line-up of UL rods, well under your price limit. Match that with a 2920 Pflueger President (about $50.00) and it doesn't get much better. JMO!

St. Croix, both premier or triumph would be around your price range. They make fantastic rods and I like their ultralights more than their bigger rods. Lifetime warranty, you can't go wrong.