Cash, Caché, Kaysh, Cache
Ok. It’s still a mystery. I received a few e-mails about this, and I tallied votes for all three. Great help there, guys :)
“Cash” – This one is said in Microsoft training videos (as in “disk cache” etc.). It’s also in the dictionary. The Oxford Dictionary and the Macquarie (Aussie) Dictionary as, phonetically, kæ§ – where the æ sounds like the “a” in bat, hence cache). However, when the Yank on the Microsoft training video said it as “cash”, everyone in the room remarked “cash???” and sniggered.
“Cash-ay” – This one is used often too. Well, cache is from the French word cacher (to hide, I think). So maybe this pronounciation makes it sound more French. Perhaps the e has an accent (é) which gives the “ay” sound, but the use of the accent dropped off and we spell it without the accent. But this theory sounds dodgy.
“Kaysh” – Seems to be used a lot. My Microsoft instructor uses it. The rest of the class uses it. Could be an Aussie thing.
Shit I’m still clueless. I’d go with “cash”, as the dictionary can’t be wrong, but I can’t scrub the “Kaysh” pronounciation which is etched into my neural pathways.
12:15am (GMT +10.00) tomorrow 
