I know there are probably many solutions, but what's the easiest and/or most user friendly way to provide search capabilities across PDF files? I'm thinking of a webpage that links to several PDFs and I want to offer the user the ability to search them all at once.
You should consider a content management system, which allows this feature. - While many do not include this feature out of the box, many of these open source CMS engines have vast amounts of useful plugins that can extend the engine to support or this type of things.
Using two of the most popular CMSs as an example
As I mentioned in the previous paragraph about plug-ins and extensions, it's worthwhile searching through the plug-ins sections of various open source CMSs for suitable add-ons.
Joomla PDF extensions that may do the job:
OS PDF Indexer - indexes PDFs and makes them searchable using the JOM Search platform.
PDF Indexer - Allows PDFs to be indexed and searched via the Joomla/Mambo search module. (Joomla 1.5)
Wordpress PDF extensions
There are far too many to list them all, but here is maybe a suitable one, which looks good: Google Document Embedder. Kinda good, if you want some way of easy management of your PDFs never mind the fact that it's stored on Google, which is a plus.
There are a handful of CMSs that will do this for you, and if you don't want to use a plugin, then you will need to code your own, or find a CMS out of the box that does this. Using Google is your best tool here and use search phrases like "PDF Indexer and Search Wordpress"
Adapting your own platform to support PDF searching
I found some information for you on Stack Overflow, and it contains various php snippets for extracting PDF text using PDF which should be useful to you. Additionally, they have a link to a blog about reading PDF and DOC files in PHP, which again will be helpful. If you want to read more, take a look at Stack Overflow's search through pdf files with php
As mentioned in my comment, I don't think there is any quick and dirty way of doing this without a heavy amount of coding, you will need to use PHP as I do not think any JS solution exists.