I need a new computer. in A Life Uncommon

Smart people of the internet, I need a new computer. I think I am pretty sold on going with a desktop vs laptop. No sense in two, and I really need my computer to WORK. I run a handful of programs at the same time (nothing huge, but I do need Skype to work while I have mutiple Excel books, doc files, etc open, AND be able to work online). Processing, that's the word I want, right? I forget how to talk computer but I need one that WORKS. I want to be able to access youtube without needing to close my files and then never switch tabs. I'd love to be able to properly WORK.

Also, I'm investing in a second screen along with said desktop, so recommendations there help too.

Go go gadget, community!