If you can connect to your Camcorder from iMovie then you already have the software in your mac. If you don't see it in your mac and you brought your Mac recently, then what I heard is if you call their support they give you the link to download the whole suite for free which comes with some other good stuff like garage band etc.
But if the iMovie cannot see the Videos from your camcorder then its all depending on how much you would like to spend. Given the iMovie has some issues/limitations connecting some of the latest Sony Camcorders, there is no choice left for you other than spending some good money. Since I haven't used any paid software I cannot give you the specific reviews but if you can learn Adobe Premier Pro its a good option else there is Sony Vegas Pro, Final Cut etc but all cost a bunch of money.
If you have any kids that are in school then you can get Adobe for the educational pricing for up to 80% off the regular price. I haven't checked Sony yet, they also may have educational pricing. I myself looking for some good software and waiting for the Adobe to give out some more discount. During the beginning of the school year Adobe had some special discount on top of the educational pricing. I should have bought it then but didn't. Now I am waiting to see if they have any Christmas present for me and my kids. :) Because I do not use the software for professional reason I do not want to spend too much on them. I want it for my experience and kids can do their school projects and learn at the same time. You can download their 30 day trial and if you like it then you can buy it. But keep in mind that if you buy Adobe educational series then you have to make a choice like whether you need Mac only or Windows only. They make you pay for each platform which sucks in my case because I have both Mac and PC.