An informative speech may be a five minute overview of an object or an event, a three hour seminar covering an abstract concept, or anything in between. But it's true that virtually any informative speech will benefit from good supporting information. General Reference resources are a good place to start.
Nothing makes an argument more persuasive than a solid factual base. Use the library's collections to get statistics, research, and other information to craft the best possible argument.
If you choose a career that does not involve giving presentations, special occasions may be the only time you will be called on to make a speech. In any event, these can be the speeches that matter most to people. And though the main content of the speech will likely be personal, you may want to bolster your speech with a quote, statistic, or by comparing it to a current or historical event.
He rang'd his ropes, and preach'd up patience; Back'd up his opinions with quotations. -Matthew Prior, "Paulo Purganti and his Wife"
Quotes are widely available on the web, but consider consulting a book (or an online book through the library) to dig up an obscure quote. The print books have the advantage of having very thorough indexes to help you get the perfect quote.
Build a base of knowledge about your topic. Full-length books provide the most in-depth coverage and perspective over time, but an encyclopedia entry or book chapter will often provide sufficient background information.
...Statistics! 9 out of 10 speechwriters find that statistics are an essential part of winning any argument. However, 34% of statistics are made up on the spot (source? HA!) Follow the links below to get accurate numbers from authoritative sources.
If you want to relate the occasion that your speech is meant to commemorate to a current or past event, try searching news sources to get an overview of those events.