A lot of benefits can be had from handing the players index cards, handouts, notes, et cetera. Is there a good way to simulate this online? We play with IRC and a virtual tabletop (d20pro), but I'm envisioning maybe some cloud system we could use for organizing that sort of thing so we can quickly reference, say, the text of a message we received or a bit of text from a library.
You might look into using a Wiki.
For the campaign that I've been developing, I have a Wiki that is separated as such:
This has worked out great for me. I have one central place to go when I'm working on adventures, I can link between entries (ex: I have an adventure where the players go to the temple of a specific god, and the adventure description has a link to the entry for that god) which makes it easy to find information, I can keep information separate between what I (as the GM) know as compared to what the players know--and simply move it into the player area when I'm ready for them to have it, I can upload and share images just as easily as text, and the players can make their own notes in the player area on the things they think are important or want to remember.
An added benefit is that many people already know how to use a wiki, so the learning curve for them is very low.
Evernote is a good candidate for this. It's a cloud based note storage tool, handling text (with tagging and some formatting), images, and some other types of document attachments. It's got clients for pretty much every major platform (including phones and tablets), and a web interface.
Notebooks can be shared between users. The free version allows read-only sharing, so one person can post the notes and everyone (who you grant access to) can view them. A paid account allows granting write permissions to shared users.
I've used it to keep track of notes in my campaign, sharing things with other collaborators in writing up some documents. If you want to share notes with everyone, it's a very easy to use tool to accomplish the goal. It's more cumbersome to share with only specific people, but still doable.
For what you want I think it'd work well, as it's really good for storing bits of information you find during a campaign, and then tagging & categorizing them later.
Roll20 has a feature allowing to create notes (even with images) and give access to them to the players you choose to.
I'm not familiar with every IRC interface out there but I know at least some have the option of creating private chats (Private Message). You could upload all your handouts in some place that makes it easy to fetch the links to that info and post the links via PM.