Does anyone know of an application that will scan an org to determine the remediation necessary to enable multi-currency? Scanning for things like Currency fields used in SOQL calls and currency fields used in formula fields would be easier than having to look manually.
I'm not aware of a tool like this, but in general for this sort of impact analysis I'd recommending installing some flavor of SFDC development environment (Force.com IDE, Sublime Text + MavensMate) and downloading all apex and objects. Then it's just a matter of doing a text search across all the downloaded files for currency fields.
Note I'm only focusing on your question about how to check for currency fields in SOQL and formula fields. There could be other requirements for enabling multi-currency you'll want to consider.
There are numerous applications on the App Exchange and Chrome Plugins that will scan an Org's metadata, including code, workflow rules, validation rules, etc. None are going to be specifically configured to exactly look for multi-currency fields. One App Exchange product that comes to mind which I've used in the past is Octopus. Another is Metadata Search for Salesforce. There are too many new Chrome plugins that will allow similar functionality for me to list.
You'll also want to consider what is going on architecturally with any custom code you might have in your org that does currency calculations. I would specifically recommend you try to focus on triggers, controllers, classes and asynchronous code that reference opportunities, oli, quotes, qli, schedules, products or pricebooks along with accounts and any custom objects that also include currency fields.