There are a plethora of websites available for research and I'll list a few of my favorites. But, I'm always asked about books I've found helpful so I thought I'd list a few of my favorites. This is a list in progress and I'll add to it as I find books I feel are very helpful.
The Writer's Market (Writer's Digest Books) - a great reference for publisher information.
First Draft in 30 Days (Karen Wiesner) - great tips and tools for turning off the Internal Editor and just writing.
Writing The Breakout Novel (Donald Maas) - incredibly helpful in finding your voice and writing the book of your heart.
On Writing (Stephen King) - he opens up about writing, writing and writing.
Specific to the romance genre:
Complete Idiot's Guide to Writing Erotic Romance (Alison Kent)
Writing A Romance Novel for Dummies (Leslie Wainger)
Books for research:
VGM's Career Encyclopedia - check your local library. This is a great reference for career information. It won't take the place of talking to an actual police officer or doctor but it's a good start!
Character Naming Sourcebook (Sherrilyn Kenyon) - a great resource for names and meanings.
Frommer's USA and National Geographic's Guide to Scenic Highways & Biways - these are two great references for different areas of the United States. If you don't have the money to travel to every area you write about, you'll find a wealth of information in these two guides.
Police Procedure & Investigation (Lee Lofland) - a great reference for suspense writers. Again, it doesn't take the place of actually interviewing a police officer but it's a great place to begin!
Kristina writes sassy contemporary romance novels; her books have appeared on Kindle Best Seller Lists.