Wildflowers of the Pacific Northwest

by Mark Turner & Phyllis Gustafson

Definitely the best book out there for the Pacific Northwest. While it doesn't have everything (no book does), it's easy to use and has photos and maps for every species.

Plants of the Pacific Northwest Coast

by Jim Pojar & Andy MacKinnon

Provides a ton of detail about many of the plants that grow west of the Cascade crest, including many ethnobotanical anecdotes. An excellent resource for identifying shrubs and trees, as well as some ferns, mosses, and lichens.

Alpine Plants of the Northwest

by Jim Pojar & Andy MacKinnon

Similar to Plants of the Pacific Northwest Coast, this time covering the subalpine and alpine zones from the Cascades eastward.

Plants of the Rocky Mountains

by Linda Kershaw, Andy MacKinnon, & Jim Pojar

It's a little out of our bailiwick, but another fantastic resource from Pojar & MacKinnon, this time joined by a third author.

Wildflowers of the Columbia Gorge

by Russ Jolley

This somewhat outdated book is locally well-loved, partly because its author was well-loved, but it's not easy to use and its organizational scheme is a mystery. It's perhaps most useful for its tips on where and when to find specific flowers.

Trees and Shrubs of the Pacific Northwest

by Mark Turner & Ellen Kuhlmann

Because you may stumble across a few plants that aren't wildflowers.

Mushrooms of the Pacific Northwest

by Steve Trudell & Joe Ammirati

...and sometimes you find things that aren't even plants.

Flora of Oregon

A multi-year, multi-volume project from OregonFlora. Volume 3 is expected any day now.

Flora of the Pacific Northwest

by C. Leo Hitchcock & Arthur Cronquist

Mostly key-based — rather than full descriptions of each plant — so you have to be really committed. (FYI, the Multnomah County Library has several copies available.)

Flora of North America

There are (or will be) 30 volumes, and each one costs about $100. Probably better to just look at the FNA Web site... or access the data right here.

"100 Hikes in... Oregon" (series)

by William L. Sullivan

Frequently-updated series of hiking & travel guides that feature detailed hike descriptions and surprisingly helpful hand-drawn maps.

Day Hiking in Washington (series)

There are 12 (or more?) books in this series that's affiliated with the Washington Trails Association. They're handy to have in the car while on a Washington road trip, just keep in mind that they make every hike sound a little too good to be true.

Washington Wildflower Hikes: 50 Destinations

by Nathan Barnes & Jeremy Barnes

A decent collection of hikes with lots of glossy photos, but they lose points for featuring several non-native plants. (Sadly, the authors are not the same Barnes & Barnes who gave us "roly-poly Fish Heads.")

Oregon's Best Wildflower Hikes: Southwest Region

by Elizabeth L. Horn

A bit out of date (i.e., some of these trails have mostly vanished), but it covers a lot of hikes that you might not hear about anywhere else. Long out of print, so keep your eye out for a second-hand copy.