yardsellr has some nice transitions and animation, as well as a tour invitation to get started. Super short listing form for sellers. Nice implementation of auto-suggest in the search field.

What would make this app even more fun to browse, is if there was a way to quickly flip through all the pictures in a category— kind of like when you are at a yard sale, and you rummage quickly through all the items. Or complementing live scroll (like Google images) instead of paging would make it quicker/easier to scan all the listings.