I have what I'd call a form of pseudo-synaesthesia: I don't experience crossed senses, but I have strong, involuntary, consistent associations between different sensory modes.
Examples:
I have associations between musical key and colours (there's a clear relation to the circle of 5ths there, with, generally speaking, flat keys becoming darker and adding more blue, purple and black, and sharp keys becoming more complex colour mixes), and in one case, temperature.
I have associations between letters and colours.
I have associations between days of the weeks and colours (I got an appointment confused once because Monday is a very similar colour to Wednesday) , and between days of the week and musical keys.
These associations are so strong that, for example, if I'm playing a piece of music in E flat major, I forget that the sheet music doesn't literally have a darkish blue cast to it, and that the notes affected by the key signature are not highlighted in blue. (And I have to remember not to say things to my students like "of course it's in G major; can't you see the light sky blue?".)