The new taskbar in Windows Mobile 6.5.3 no longer activates the start menu, but drops down a set of notification icons. I believe Microsoft missed a significant opportunity to add a Pre-like task manager there, and I am not the only one who thinks this area can do more.
RAMMANN on XDA-Dev has created Taskbar launcher 0.1 which creates a customizable drop down launcher which pops up when you tap the task bar.
The software is only intended for WM 6.5.3 and works for VGA and WVGA resolutions.
It is still a work in progress, and currently to change the apps one has to edit a text file, but the developer intends to make the process a bit more slick in the future.
Read more about the app and download it at XDA-Developers here.