Sounds like you're the IT Manager.
I'd go with sys admin, echoing other's thoughts.
However, depending on how much you respect your users, how about muppet wrangler?
To me, IT Manager implies a role consisting primarily of people / services management. Systems Administrator implies more involvement and oversee in the technical delivery.
Which is one "best" probably depends more upon what Dave wants to be seen as and where he wants to go in future.
As the IT Manager has gone and will be replaced 'at some point in the future', my guess is that Dave!!!!! will have to do the guys job as well as his own. So aim big!
Thanks everyone. "IT Systems Administrator" is likely to get the nod I reckon. The reason for the lack of a manager is that we're due to merge with another company, there's already collaboration, and the other company is keeping their IT manager (who eventually will become our IT manager I presume). So for now, we report to the finance director until the merge gets done. And I was ideally wanting a permanent job title, rather than an "Acting" position.
Although "BOFH" came in a close second....
Before you settle forĀ "IT Systems Administrator", consider "Velma".