quicklisp - library manager - BSD - portable
quicklisp is a library manager compatible with all major common lisp implementations. It will handle downloading, installing, and dependency resolution for over 700 common lisp libraries. It is similar to a linux package manager like yum, apt-get, or pacman.
Although quicklisp is still in "beta" it is well developed and has good integration and testing across many OSes and implementations. There is little reason not to use it. It makes a project of any size much easier to manage.
hunchentoot - webserver - BSD - portable
hunchentoot is a pure, general purpose common lisp webserver portable to all common lisps. It supports keep-alive, SSL, automatic session handling, logging, and multiprocessing. It does not come with any HTML generation facilities.
hunchentoot allows for customized request routing based on generic functions and also provides functions for easily creating pages and coercing URL parameters into variables.
I've found hunchentoot to be pretty easy to work with and a generally solid webserver.
cl-who - programmatic HTML generation - BSD - portable
cl-who is a fast HTML generation library for converting s-expressions into HTML. cl-who is designed to be fast by compiling the longest constant strings possible. It is built on a macro which converts common lisp symbols into HTML tags. It is not a templating library.
I've found cl-who to be fast and moderately easy to work with. Being a macro it takes more thought, at least initially, to get what you want compared to a pure functional approach and sometimes doesn't inspire the most clear or concise code.
I've found parenscript to be well developed but have run into portability issues on CCL/clozure.
ironclad - common lisp crypto lib - MIT - portable
ironclad is a cryptography library written in pure common lisp. It supports many of the most widely used ciphers, digests, key derivation, and MACs. It includes support for basic public key cryptography and gray streams. It does not handle strings.
ironclad provides common lisp password hashing with scrypt and pbkdf2.
I've found ironclad to be by far the most well developed, tested, and usable encryption library for common lisp. Importantly for web development it is also, as far as I know, the only common lisp library that supports password hashing via scrypt and pbkdf2 which are the current best practices for securely storing passwords. Due to the complications of UTF and strings it does not deal directly with strings.
Supported password hashes / key derivation functions:
practical common lisp - free common lisp book
Practical Common Lisp is an excellent common lisp book by Peter Seibel that covers beginning to moderate level common lisp development and includes a large number of in depth practical examples of real world usage.
lisp for the web - tutorial on modern common lisp web development
A good beginners guide to developing web applications with hunchentoot, cl-who, elephant, and parenscript.
Also a good beginners guide to developing web applications designed as a continuation of the original lisp for the web tutorial but by a different author.
It covers cl-who, hunchentoot, parenscript, elephant, fiveam, css-lite, and cl-json.