Two brands popular with bicycle tourists are
Arkel and
Ortlieb . Both will keep your stuff dry, though by different technology. Arkel bags have a heavy duty cordura body with exterior covers and interior dry bags. Ortlieb has a waterproof exterior. Both make excellent, top of the line products. You couldn't go wrong with bags either company.
Both my wife and I use Arkel bags for touring. Arkel products have a lifetime, transferrable, no receipt required guarantee. I personally prefer the Arkel interior design for organizing things and believe the Arkel mounting system is easier to use and is more robust than Ortlieb's ... but others might (and probably will) disagree.
Here's my bike with
Arkel bags