If you are looking for a tool where you can upload a photo, then add a really nice looking caption with various fonts and effects, Caption Day is a solution to it.
Memes + Contest = Riches
It is an online captioning tool where user can choose an image and apply caption on it. It also has the scope creating competition set by admin. On winning, one can have badges.
Donate with Captionday!!
You can also make donation and what not. It has one of the excellent UI. User can put caption on photo with different fonts and styles in various positions. Most of the online captioning tools are just limited. It is flexible easy to use captioning tool.