Web design galleries serve multiple purposes. First, they are great for web designers looking for idea for future projects. Secondly, they work well as display windows for anyone responsible for a creative website design. In addition, I believe that SEO professional also use these websites for getting a few back-links, but I really doubt the effect of this.
Some of the web design inspiration websites have additional features such as tags/categorization, awards and user ratings. This is useful to get a quick overview of website designs that stand out and what people like most in various niches.
I have found more than 40 website that all focus on featuring web design one-way or the other. I am sure you will find the resource comprehensive and that there will be design galleries you can use. However, please let me know if I missed a great website and share the article with people you know.