Are there any fonts I can count on being on the user's system?
I'm talking typical fonts like Arial, can I safely assume that it will exist? Or do I have to manually embed the ttf?
I continually end up on this site when I find myself asking this question.
Here you can find the list with the standard set of fonts common to all versions of Windows and their Mac substitutes, referred sometimes as "browser safe fonts". This is the reference I use when making web pages and I expect you will find it useful too.
Although the page refers to web pages, you can apply the list to any application.