I like the Antibes and JuanLesPins themes from the Beamer class. They use a nice tree-like navigation at the top, which provides a good notion about where exactly the speaker is in her/his talk. This feature is especially important for presentations given in places where attendees don´t care too much about being in time.
Antibes and JuanLesPins use the tree and smoothtree “outer” themes. The problem for me is that they provide a 3-level tree navigation (Title, Section and Subsection), plus the Frame Title. I don´t have subsections in my presentations. Also, I don´t think it´s necessary to have the main title in every single frame (but if you enjoy it, try using one of the nice beamer footer instead, for example the one from Madri theme).
Unfortunately I couldn´t find any beamer theme with Section plus Frame Title only. So, a very simple cleanup in the tree outertheme gave me what I was looking for:
If you want to use this, just set it as the outertheme in your tex. Supposing the file name is beamerouterthemesingletree.sty and it´s located in the same directory as your tex file, add: