The best part about Apache is that you can custom build it to include exactly what you need. The defaultconfiguration is a good one, but its far-too-general nature is, by definition, not the best choice for the majority of installations. With a host of plug-in modules available for free over the Internet, customizing Apache to its fullest extent is not only fast and easy, but well worth the time spent.
Modules can be grouped into a few major groups: Access Control, Authentication, and Authorization; Header-generating and -controlling modules; Content generating (or filtering) modules; and Utility modules. The descriptions come from the Apache Documentation, but the groups are mine (you'll probably never see anything like this in the official docs, but I find it easier to categorize them this way). Items in bold are enabled by default.
Content Generating and Related Modules
mod_autoindex provides for automatic directory indexing.
mod_actions lets you run CGI scripts whenever a file of a certain type is requested. This makes it much easier to execute scripts that process files.
mod_dir provides for "trailing slash" redirects and serving directory index files.
mod_imap provides for .map files, replacing the functionality of the imagemap CGI program.
mod_include provides for server-parsed html documents.
mod_isapi provides support for ISAPI Extensions when running under Microsoft Windows.
mod_mime provides for determining the types of files from the filename.
mod_mime_magic attempts to determine the MIME type of a file by looking at a few bytes of its contents, the same way the Unix file(1) command works.
mod_mmap_static provides mmap()ing of a statically configured list of frequently requested but not changed files.
mod_speling [sic] attempts to correct misspellings of URLs that users might have entered, by ignoring capitalization and by allowing up to one misspelling.
mod_status allows a server administrator to find out how well their server is performing.
mod_userdir provides for user-specific directories, in the form http://www.server.com/~user/.
Access Control, Authentication, and Authorization Modules
mod_access provides access control based on client hostname or IP address.
mod_auth provides for user authentication using textual files.
mod_auth_anon allows "anonymous" user access to authenticated areas.
mod_auth_db provides for user authentication using Berkeley DB files.
mod_auth_dbm provides for user authentication using DBM files.
mod_digest provides for user authentication using MD5 Digest Authentication. It is replaced by mod_auth_digest.
mod_auth_digest provides for user authentication using MD5 Digest Authentication. It is an updated, though untested, version of mod_digest, with many more options.
Utility Modules
mod_alias provides for mapping different parts of the host filesystem in the the document tree, and for URL redirection.
mod_info provides a comprehensive overview of the server configuration including all installed modules and directives in the configuration files.
mod_log_config provides for logging of the requests made to the server, using the Common Log Format or a user-specified format.
mod_proxy provides for an HTTP 1.0 caching proxy server.
mod_rewrite provides a rule-based rewriting engine to rewrite requested URLs on the fly.
mod_so provides for loading of executable code and modules into the server at start-up or restart time. On Unix, the loaded code typically comes from shared object files (usually with .so extension), whilst on Windows this module loads DLL files.
mod_vhost_alias provides support for dynamically configured mass virtual hosting.
Header Generating Modules and Header Control
mod_asis provides for .asis files. .asis files have headers prepended to the content and are sent, well, as is.
mod_cern_meta provides for CERN httpd metafile semantics
mod_env provides for passing environment variables to CGI/SSI scripts.
mod_expires provides for the generation of Expires headers according to user-specified criteria.
mod_headers allows for the customization of HTTP response headers. Headers can be merged, replaced or removed.
mod_negotiation provides for content negotiation based on, for example, language preference or browser type.
mod_setenvif provides for the ability to set environment variables based upon attributes of the request.
mod_unique_id provides a magic token for each request which is guaranteed to be unique across "all" requests under very specific conditions.
mod_usertrack generates a 'clickstream' log of user activity on a site using cookies.
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