Googling for "financeferret" did not turn up any apparent trademarks in ~2008. The domain name "financeferret.com" was registered in 2006, but as of 2008-08-17 the associated web site still showed it as "coming soon" -- possibly a domain squatter.
From this, I determined that the name is more or less available for this use. "financeferret.net" and "financeferret.org" were available as of 2008-08-17, but it didn't seem worth the trouble and expense to register them (enough just-for-the-name domains sitting around sucking $12/year out of my bank account already).
When I checked again on 2009-06-06, financeferret.com had become available, so I registered it... but later let the registration expire. As of 2011-09-27 it was still available, but it seems to have been registered by someone in Australia on 2015-04-17 (domain parked with no advertising).
As of 2017-07-08, it redirects to financeferret.com.au, a web site for "Finance Ferret Pty Ltd" which appears to be a trade name registered in Australia. The .org and .net domains remain available as of 2019-08-22 (and of course a much larger number of TLDs are now available, if those are ever taken, assuming FinanceFerret ever really needed its own domain).