Tycho of Penny Arcade plugged Scary Go Round a few weeks ago, calling it something like "as good as comics get." I don't know if that's true, but it is very good. It's taken me a few sittings to really get into the swing of things, given the multitude of characters and complex continuity, but now it's sucked me in and wasted pretty much my whole evening.
At first the art seems kind of stiff and the rhythms of the humor feel a bit odd. It helps to realize that the strip is British, and you should read the characters' lines with an English accent in your head, with that dryness that the English bring to absurd situations. In some ways it's reminiscent of South Park with its brightly colored, flat-looking art style, as well as its casual use of supernatural elements and cartoonish violence for comic effect. The characters, however, are not only older and cuter, but much more on the likable and charming side.
When you go to the site, you'll find fourteen boxes at the bottom of the page, each of which represent a different story arc in the series. I recommend starting with a couple of early ones ("Fair" is a particularly good jumping-off point), and giving yourself a couple of story arcs to get used to it. The cuteness and the Britishness make me think that Lydia and Sarah especially would like this (assuming Sarah's not reading it already, either through the same Penny Arcade connection that introduced me to the strip or her own extensive webcomic reading).
If you do like it, you can eventually explore the less-pleasantly-drawn origins of the characters in the Ur-Scary-Go-Round strip, Bobbins. Seriously, though, the art is pretty ugly, so don't go until you already love the characters for their personalities.