I agree that the sudo mechanism - in windows the User Account Control dialogue - is a good way for an account to have the potential to act as an admin, but without always having the ability.
On one of my forums, the approach I use is to have an admin login, but usually to use Impersonate User to login as a normal account always all the time. When I need to act as admin, I logout and login again. This does mean two accounts.
One advantage of two accounts is that when I post or comment with my normal account, I do not appear as a powerful important person. (Sometimes, commenting as an admin will be taken as a pronouncement or a police action. It depends on the culture and expectation of the reader.)