Something to consider ...
Domains are not "rented", but are intangible property in the view of many, including some court opinions.
The annual renewal fee is basically a maintenance fee.
If domains were "rented", the renewal price would vary greatly (ie. like .TV domain registrations) and furthermore, the registrant would not be considered the "owner" (some may debate this aspect since some registrars state otherwise in their terms) ... how else could people "sell" domains, if they don't actually "own" them? One can debate this for sure, but point is that the renewal fee, in the view of many experienced domainers, is NOT rent.
It's important to be consistent ... treating a domain itself (content is a different matter and should often be considered separate) as an expense will likely result in much higher tax liability upon sale ... or worse if one treats it as an expense in some parts and at same time an intangible asset elsewhere in their accounting - regardless of how one defines a domain for accounting purposes, it's important to be consistent.
There is no one simple answer for domain names as of yet ... most taxing authorities have chosen to steer clear of defining exactly how a domain should be accounted for.
So in short, one way to account for the renewal fees would be to add it to the cost basis of each of the domains renewed. That may not help much now, but likely will upon sale, since a higher cost basis will typically reduce the gain incurred.
Do some searching around on the forums - there have been numerous discussions about domain accounting.
Finally, if you are doing more than say $xxx in renewals and/or expect to do $x,xxx or more in sales eventually, consider hiring an accountant (not tax preparer) for professional advice regarding the various accounting methods - there's more than one way to treat a domain name depending on one's exact business ... ie. a domain registrar would likely treat domains little more than a "service" while a domainer would potentially treat them as simple inventory or intangible property, etc.
Ron