Dropbox Automator is IFTTT for Dropbox. Takes actions based on files being saved in to your dropbox folder(s). Get started at http://www.dropboxautomator.com
The Dropbox photo gallery RSS feeds are currently (Nov 2011) broken, this mini-app provides a working solution. Full instructions are found on the Dropbox Forums.
Busyflow allows you to collaborate effectively using cloud apps, including Dropbox. BusyFlow is a workspace that creates the easiest way for you and your team to collaborate and manage cloud apps. Get started at http://busyflow.com/
300milligrams allows you to connect with Dropbox and other popular cloud productivity services and receive notifications. Find out more at https://300.mg/
Jotforms allows you to get people to send files from your website to your Dropbox. Find out more at http://www.jotform.com/dropbox/
Airdropper is a web application that allows Dropbox users to request a file from anyone, even if the person doesn’t have a Dropbox account. You can get started at http://www.airdropper.com/
Fuzli allows you to build your own fancy photos gallery from your Drobox folder (iPhone & iPad compatible). Get started at http://fuz.li.
Otixo allows you to cut, copy, and paste files between Dropbox, Google Docs, SugarSync, FTP, and WebDAV. Find out more at http://otixo.com/
CloudHQ allows you to backup and sync Google Docs and other cloud services to Dropbox. You can find out more information at https://www.cloudhq.net/dropbox
KISSr enables you to host websites using your own domain name. KISSr is free to use for for third level domains (eg. yourdomain.kissr.co) and has very affordable rates on second level domains (eg. youdomain.com).