Here are the fonts I use: Sans (size 10) in the Openbox menus and window titles, MgOpen Cosmetica (size 12) in the gtk themes, and in the earlier screenshot Dreamspeak (size 12) for the menu header and the on-screen-display (alt-tab and desktop switcher, which is not visible in the screenshots, of course). In the second screenshot, dreamspeak is replaced by Sans (size 10) in the menu header.
BBtime (the clock in the dock) uses that ugly Helvetica font, because I'm not able to change the font of it for some odd reason. The font on my wallpaper is Lohit Bengali.
MgOpen Cosmetica and Dreamspeak only look nice in size 12 (and upwards) on my laptop. I quite like dreamspeak, but not its upper-case letters.