Here are six of my most used and favorite resources:
And no, it's not the thesaurus or dictionary. Although the link should take you to a pretty good one online.
I got this tip from writer DiAnne Mills when she wrote her Leather and Lace historical romance. All kinds of info can be gleaned from this source and if your library does not carry it and you like to write historicals, you can pick up a set for around $200 on E-bay for a 26 volume set.
I have a site I use to calculate what something was worth then compared to now and vice versa. It helps when you're trying to figure out how much your hero would have paid for that ring back in 1855. Or how much that horse would be worth by today's standards.
I write historicals and for that authentic feel, I like to browse letters of soldiers so I can get a feel for the language of the times, as well as movement of troops etc. There's a lot of info here that good people took thousands of hours to document.
6. Words of the Times
No matter what timeline you write in, chances are you want to put expressions into the character's mouth that by etymology research, they could not have said. At least in that way. A good Etymology source should be open on your desktop at all times for quick reference. Why? Because like other kinds of research, we have some pretty smart readers out there who will know.
Okay, I've given you my top 6 now what's yours?
ginger r. takamiya