Welcome to the Q&A Forum

Actually it depends on the content and site intent. Taking Tyler's suggestion further, If there are several products or services in each primary category then it could be: domain.com/dodge/ domain.com/dodge/viper.html or domain.com/dodge/ domain.com/dodge/viper/ domain.com/dodge/viper/roadster.html domain.com/dodge/viper/sports-coup.html Also, using "car" in the URL as Tyler suggests only makes sense if you are targeting the broad "car" related searches, or if you have categories such as "cars", "trucks" etc.  And if you do, having domain.com/cars/ would be better than domain.com/car/ In any event, you also need to consider user experience - stuffing too many keywords in a URL can become ugly. Do it right and you can get the additional benefit of Google including your URL structure in the SERP in a way that makes it look like breadcrumbs - replacing the URL shown.

Product page www.birdproduct.com/birds/blue-bird Blogs www.birdproduct.com/blog/how-to-spot-a-blue-bird-in-spring www.birdproduct.com/blog/what-do-blue-birds-like-to-eat www.birdproduct.com/blog/5-ways-to-prevent-your-cat-from-eating-up-a-blue-bird www.birdproduct.com/blog/the-best-pictures-of-a-blue-bird-you-have-ever-seen On each of these blogs you'll have a link to the product page with a link that has 'blue bird' or some variation of it to the product page. This way your product pages doesn't have to compete your blog for the short term keyword 'blue bird', while you'll still get long tail traffic for your blog titles and have a nice internal anchor text pointing to your 'blue bird' optimized product page. The canonical page in this case is simply the url, as there are no parameters or whatever 'exclude' for Google.

Tony, whether or not you decide to index these categories you won't be losing any strength on the already indexed pages. The non-indexed pages already have juice flowing to them - you just can't see them in the SERP