Here is a list of all documented variables with links to the documentation:

rate_change_buffer : spike_source_poisson.c
recording_flags : c_main.c, c_main_neurons.c, c_main_synapses.c, spike_source_poisson.c
recording_info : neuron_recording.h
recording_values : neuron_recording.h
reset_address : neuron_recording.h
rewires_to_do : spike_processing.c
rewiring_data : topographic_map_impl.c
rewiring_recording_index : topographic_map_impl.c
ring_buffer_mask : synapses.c
ring_buffer_size : synapses.c
ring_buffer_to_input_left_shifts : neuron.c, synapses.c
ring_buffers : c_main.c, local_only.c, synapses.c