Skógafoss (Skogafoss without the Icelandic letters) rivals Gullfoss as Iceland's most famous waterfall. It drops 60m with a width of 25m and has a classical rectangular shape prompting my wife to call this her favorite waterfall in Iceland.
Besides the aesthetics of the falls, it's also very easy to access its base so you can always expect crowds of people here. There's also a path leading to the top of the waterfall where it then continues along the Skógá River where several other major waterfalls can be found.
Look for this easy-to-spot waterfall along the Ring Road about 105km east of Selfoss (the town) and 103km west of Kirkjubćjarklaustur.