Okay, so Logitech have announced the M330 Silent Plus and M220 Silent. Although technically not silent, they are meant to offer 90% less noise, supposedly to stop bothering your office mates or even family members in the same room. Apparently shipping in September and starting at £29.99 in the UK.
I am REALLY not sure how I feel about a silent mouse! Anyone else think it would break your head a little bit to start out? If it was the same with a keyboard, I think i'd actually have to start shouting "CLICK" at every press.
M330 Product page - Here
M220 Product Page - Here