I need stories of infedelity discovered through ingenious or bizarre
means. Accidental discoveries especially.

suspicious hair in the hot tub or pool filter

There was this guy who thought his wife might be cheating.  She'd been
particularly disrespectful in the preceding years and grown colder in
the relationship.  Behavior always being the more truthful than words,
he began to suspect her.  At one point she all the sudden decided to
lock her e-mail account with a password.  Her husband thought that odd
and unnecessary as the only person it would likely lock out was him.

Soon after he confided in a friend, who knew about computers, his
concerns about his wife's secrecy.  His friend insisted that he get
into his wife's e-mail.  That was the only way to know the truth. 
That friend told him that he could use a device called a keykatcher to
find out what she was writing in the e-mails.  A keykatcher is a small
piece of computer hardware.  It's a memory device that captures
signals directly from the keyboard before they enter the computer. 
Thus, it cannot be detected or thwarted by software protection.

The next day a message from the wife was discovered and it was nothing
less than a steamy love letter.  Another cheater was caught!