If you are on a Mac there is no substitute for Omnigraffle. in the PC world a lot of UX designers use Visio I am not a big fan of it, but it does get the job do

If you are on a Mac there is no substitute for Omnigraffle. in the PC world a lot of UX designers use Visio I am not a big fan of it, but it does get the job done. There are a good deal of online tools as well.