What is a "good crawlable design"?
Don't use flash - flash is SEO suicide. Some say the search engines can crawl flash but even if they can they certainly can't crawl it as well as HTML. (See below).
Interlink your pages - search engines find your pages by following other links in your pages. Be sure to link to your pages liberally especially important pages.
Use search engine friendly URLs - Although search engines can crawl query strings just fine, using a URL that appears static is a good thing. Errors can occur on long or complex query strings and this eliminates that possibility plus it is a great chance to get keywords into your URL
Use semantic markup - HTML is a powerful tool that search engines use to determine the context of a page (that's another reason why flash sucks for SEO: no html). Use HTML properly to give keywords more weight within your pages. See the Search Engine Optimization FAQ for more on that.
Use a sitemap - sitemaps make sure your pages are easily found by the search engines (good for humans, too).