I personally prefer a separate good task manager and a separate information management/reference application, than something that tries to do everything and ends up being simply mediocre. You can find long discussions at
http://www.outlinersoftware.com on this issue.
In this regard, I find that GQueues' ability to enter URLs in the notes field (as well as create a task from an email and maintain the link to that email) is more than enough to reference the information needed for a task. For example, to link to a Google Docs file, all you need is its URL.
Most of all, GQueues' unlimited subtask level ability means that any item I create is always in context within the greater project view.
I have seen tighter integrations, e.g. Nozbe's with Evernote, but I am not sure that they are as useful in practice.