If we can not shrink the transistor size any further, what other options do we
have to increase compute power?

3D packaging

The ITRS report suggest to go into third dimension and build cubic chips.
The more layers are build the more integrated cooling will be necessary.

Memory Wall

Currently memory latencies are higher than compute cycles on CPUs,
with faster memory tehchniques or higher bandwidth the gap can be closed.

Memristor

The Memristor is an electronic component proposed in 1971.
It can be used for non-volatile memory devices and alternative, neuromorphic
compute architectures.

Photonics

Using light for computation sounds quite attractive,
but the base element, the photonic transistor, has yet to be developed.

Quantum Computing

Really, i do not have a clue how these thingies work,
somehow via Quantum Effects like Superposition and Entanglement
but people say they are going to rock when they are ready...

Considering so much room for research,
i give +1 points for the Singularity to take off.