I'm not the most terribly creative father when it comes to finding activities for my toddler. Most of it is due to the fact that my wife worked in a daycare for toddler-age children, and through that, automatically knows what to do with kids that age. Me being the proud man that I am, I never think to ask her for ideas, but I often find that I'm at a loss for what to do with my son when we're spending 'daddy time' together while mom is catching up on sleep or running errands that have been piling up for weeks.
I think most of my lack of creativity is because I don't really understand what level of development toddlers are at during any given age, so I tend to do whatever seems to keep my son interested (which is mostly TV). I think things will be easier once his vocabulary develops a little more and he can actually ask to do certain things, but until then, I'm going to be at somewhat of a loss. I have resolved to try and come up with better activities to do when I'm spending time with my son, and found a great site that lists some age-appropriate activities that are both fun and also help with a toddler's development. The list can be found here, and offers up some surprisingly easy to organize activities that should give lots of ideas to keep in your back pocket for those days when you can't find something to keep your toddlers engaged and busy.