I know there are some that are pretty wide horizontally, but switch to a theme that isn't fixed-width and you won't have that problem. There are like 50 themes on PC so it shouldn't be too hard to find something else you like!
I know our default theme right now (Gen InVerse) is unnecessarily wide because it doesn't fit on 1024x768 which is still a popular screen resolution. :/ But I'm pretty sure it's the only fixed-width theme that won't fit on that screen size.