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Here are 3 recommendations along the lines of short and sweet, more about implementation than theory:

"Web Form Design: Filling in the Blanks" by Luke Wroblewski

http://www.amazon.com/Web-Form-Design-Filling-Blanks/dp/1933820241/ref=sr_1_1?ie=UTF8&qid=1314375416&sr=8-1

"Simple and Usable Web, Mobile, and Interaction Design (Voices That Matter)" by Giles Colborne

http://www.amazon.com/Simple-Usable-Mobile-Interaction-Design/dp/0321703545/ref=sr_1_1?s=books&ie=UTF8&qid=1314375497&sr=1-1

"Designing Web Interfaces: Principles and Patterns for Rich Interactions" by Bill Scott and Theresa Neil

http://www.amazon.com/Designing-Web-Interfaces-Principles-Interactions/dp/0596516258/ref=sr_1_1?s=books&ie=UTF8&qid=1314375754&sr=1-1

Note that these, like most books in this field, primarily focus on designing for the consumer, as opposed to, enterprise, software experience.  The issue is that all the good stuff in consumer is relevant to enterprise, but there are design issues to do with necessary complexity that are not addressed in consumer examples.  I've yet to find a good reference that does a good job with the complexity issues.

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A List Apart is a great web resource, lots of articles covering a wide range of topics from theory & thinking to making (and free!).

Their A Book Apart series is geared a little more towards folks with some HTML/CSS background. They're all short and sweet and cover some really important, emerging best practices and trends including Responsive Design.

I haven't read but have heard good things about Khoi Vinh's Grid Principles for Web Design; helpful as designing to grids has become almost standard and there aren't a lot of learning resources on the subject.

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I'd second Khoi Vinh's book, Grid Principles for Web Design.

Also...

"Designing for Interaction" by Dan Saffer

http://www.amazon.com/Designing-Interaction-Creating-Applications-Devices/dp/0321432061

"Don't Make Me Think" by Steve Krug

http://www.amazon.com/Dont-Make-Me-Think-Usability/dp/0321344758/ref=sr_1_1?s=books&ie=UTF8&qid=1314460899&sr=1-1

In addition to A List Apart, I'd also check out Adaptive Path's Blog or ixda.org

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Also worth checking out Adaptive Path's FREE iPad App featuring internal conference footage.