Ana posted a good blog about small KDE3 applications missing in KDE4 which spawned some good comments and suggestions for more apps that we are missing. Rather than let such ideas disappear into the ether I've created a wiki page for Missing Applications to try keep track. So if there's a KDE3 application that you are missing in KDE4, or a Gnome/Mac/Windows app you'd love to see a KDE4 version of then feel free to add it. Please don't just dump a list of random application names though, do a little research first to find out what the status is, what alternatives already exist and what would be the best way to do it.
Related to this is "Finding The Unloved" which the Community Working Group runs every now and then to find applications and projects that are struggling and need help, or are now unmaintained. I've also created a Finding the Unloved wiki page for keeping informal track of those. The page has separate sections for apps and projects that are requesting help, and for apps and projects the community has expressed concerned about. Please do not add anything in either category without first checking with the project or application involved, and always add a status date for your entry to help keep track of things.