First, go read my post on packing. Just trust me.
The Universal Packing List
I have tested this, and it is pretty good - a starting point for packing, it allows you to customize how long you will be away for, the weather, your activities and accommodations, in order to come up with a surprisingly helpful packing list!
Wanderlust and Lipstick is a great resource in general, and this link takes you to a couple of their top pages on packing for various trips - Thailand, women-only tours, etc.
A tumblr chock-full of packing tips and tricks and products, to help you pack lighter. Kind of addictive, but that might be the neatnik in me.
And while we're talking about packing, here is the site where a lot of pilots and flight attendants purchase their own luggage.
This list of packing lists is truly, epically, insanely large. You will find lists for every region, a lot of destinations, and though they are pitched towards what women will want to pack, many of the lists here will be helpful for folks of all genders.
Need some help for luggage issues? Here's what to do if there is a problem with getting your luggage from A to B.