I know a lot about this topic . . .
The ONLY way to accurately begin the process of ensuring the colors reproduce accurately is to use a device that measures your monitors color output across it's gamut. These are called colorimeters. They range in price from
$75.00 to several thousand. If you run more than one monitor and want to calibrate both to they are consistent with each other, then you can expect to pay a few hundred. The very expensive bundles will also calibrate your printers and scanners too.
Anyway, monitors change, and room lighting conditions change. They change more than we can tell with our eyes considering how our brains adapt to these things very well . . .
If anyone tells you that Adobe Gamma, or some other "Soft Proofing" method works without using a properly profiled monitor, then they are simply not looking to achieve accurate color reproduction.
Links to this topic:
Dry Creek Photo (great place to get started)
Luminous-Landscape
Earthbound Light
A good technical discussion I had
Articles from the guys who wrote the book, the International Color Consortium