I did a bunch of research a few months back and landed on this one as well. The electric brake is awesome. It's $125 right now but I think I paid around $105 when I got it.
Having just put in a raised garden in the last 3 weeks, I used this saw and just about any cordless drill will get the job done for drilling pilot holes/driving screws.
You could get a speed square, as mentioned, for straight cuts with the saw. I'd recommend it as they're cheap enough.
I used deck screws because why not. The garden was for my wife and I got extra points for using higher quality screws.
Are you only looking for compactness in size or maybe just weight? I got the DeWalt DWE575SB circular saw for Christmas and it's awesome. It's 7-1/4" but only eight pounds or so. It's really light and cuts like a dream. It also has the electric brake so the blade stops spinning really quickly.
I've got some basic tools, hammer, cordless drill, orbital sander, and a toolbox with basic stuff as well (screwdrivers, different pliers, etc).
Is there a difference between a large circular saw and the compact ones? I was looking at this one earlier, but wasn't sure if that'd fit the bill for something I could use at home: http://www.amazon.com/DEWALT-DWE575SB-Lightweight-Circular-Electric/dp/B007QUZ16A
Always gotta check if you can. I picked up DWE575SB on Amazon for $89 a couple weeks ago. CamelCamelCamel is super helpful when you can wait.
Why is there a rubber wheel on a circular saw?
I have one of these and haven't ever regretted buying it.
DO NOT BUY RYOBI. EVER. They're about on par with Harbor Freight.
You can get a nice DeWalt for $100 from Amazon. Home Dopey carries them too, but I'm not sure about the price there.