Search engines serve as a primary gateway to the web, and their interfaces must effectively support users' search tasks. Over time, Search Engine Results Pages (SERPs) have evolved from the traditional ''list of 10 blue links'' into sophisticated and diversified interfaces, incorporating a wide range of features to facilitate the search process. However, analyses of SERP elements often suffer from inconsistent terminology, making cross-study comparisons difficult. To address this issue, this work proposes a comprehensive catalog of SERP elements that standardizes their classification. We examined leading web search engines (Google, Bing, Yandex, Yahoo!, Baidu and DuckDuckGo), assigned consistent names to elements, and organized them into groups. In total, 143 elements were identified and classified as organic results, sponsored results, or features. By publishing this catalog on a dedicated website and in a research repository, this work provides a valuable resource for future research on search interfaces.