In your position I don't think you can do better than iMovie. I have several others on PC and Mac but I keep coming back to it for all sorts of reasons - not least it's ease of use. When I need to do something it can't do then I will do that thing in a different program and then still import the scenes I've worked on into iMovie.
Recently, I experimented with Sony Vegas (which you can use free for a month) but although it was good and also powerful, Unlike Tinam, I was disappointed with it for music videos because of timing issues. Maybe it just didn't like my PC laptop (which is quite new/powerful), although there were lots of people trying to solve the same issues when I was Googling for solutions. See how it performs for you.
In my latest video I wanted to put a picture on a TV screen, but iMovie doesn't do picture in picture so I did that in Final Cut Express (which is a much more complex program) and again imported it into iMovie for everything else. You can see that video here - it is all iMovie apart from that particular effect:
What iMovie lacks is a 1) a timeline and 2) more than one video track (for top-down compositing) - and I admit this would drive some people nuts, but I have a way of working that it doesn't bother me usually. It depends a lot on what type of videos you want to make - for example if you have footage from several different cameras that you want to sync up all through a live song then cut between them then iMovie is hopeless, so when I do things like this:
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then I have to use Final Cut for the actual editing. Vegas should be good for it - but as I said it has timing issues for me.
Certainly, don't disregard iMovie just because it's free with the Mac. It's still very powerful in its own way and you can do some quite ambitious stuff with it. Probably my most ambitious video was made between that and the animating program Xtranormal. Although it can supply premade characters to animate with robot voices, that can't cut or pan and each line of the song had to be made as an individual movie and manually lip-synched. Again, I don't think anything would have done that more easily. I also made a lot of use of the panning FX here ('Ken Burns' as they call it) and although Final Cut or Vegas could have done it - it would have taken a damn sight longer. And with the titling for example - iMovie has limited pre-set options, but you can do a nice pro looking title in seconds without having to mess about with the nuts and bolts of it. You can see that one here if you like:
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