I run a small computer shop and we are planning on using Linux on our refurbs. I personally love Debian. I believe it's the best Linux distro out there. It's very fast and has a great package manager with over 14,000 packages available. However, for an end-user it can be overwhelming. Personally, I love Synaptic. However, it doesn't seem easy enough for an end user (I've tested with one). I personally like the simple package manager Ubuntu offers in it's distro. It doesn't mention dependencies it just installs them and after it's installed it tells you where the shortcuts are on the menu. Another great package manager frontend (for end-users) I've seen is the one that comes with Linspire. It gives the users the ability to browse packages easier. However, this is commercial and Linspire is garbage (in my opinion). I'm looking for something so end-users can browse packages easily and install them.

KDE offers adept, although I haven't used it before. Synaptic is the usual one recommended.

FYI, the Ubuntu simple package manager is called gnome-app-install. I guess you could try downloading the source file from the ubuntu repositories and then compiling it on a debian system.

EDIT: Looks like someone at Debian is working on this right now.

Adept with the adept-updater for KDE would probably be the simplest way. There is also Kpackage.

Gnome has update-manager and update-notifier, that are similiar to the Ubuntu updater.
This is the GNOME software update manager. It checks for updates made
available by Debian and third parties running Debian package
repositories, and lets the user choose which to install.

Update Notifier will check for the availability of new packages for
your Debian system on a daily basis. When it detects new versions of
the packages installed on the system are available, it will add an
icon on the desktop notification area.