Hi darianva,
You raise a good question - there's no one "best" way to do this.
I would start by asking how you handle password expiry for service accounts elsewhere in your organisation? Do you have automated tools? Or do you rely on documented written processes? or some combination of scripts and processes etc?
Secondly, you could look at using machine accounts instead of a user account for your service account. Then password changes are handled for you.
Alternatively, Windows Server 2008 R2 Active Directory introduces "managed service accounts" where password changes are managed by the machine account password change process, but the psuedo-user account is managed in Active Directory.
Cheers
Ken
Microsoft MVP - Window Server (IIS)
MCITP (EA, SA), MCTS (ISA, SQL Server, Hyper-V, MOSS, Ops Manager), MCSE+Security, MCDBA