Anything higher-level, and more comprehensive than pipes/sockets?
For interprocess communication, D-Bus is the standard higher level mechanism. Both GTK and Qt have bindings for D-Bus, most desktop environments (or at least GNOME and KDE) expose various services via D-Bus, and many desktop applications can be controlled via a D-Bus interface. The system bus is also useful for finding out various low level information about the system using standard system services.
KDE4 (built upon Qt4) also includes a technology called KParts, which are often compared to Window's COM.