Or you can just use Unicode characters. I have set up my computer so I can alternate my keyboard setup between Norwegian (for regular use), US (for programming), and Greek (for greek letters):
αβγ ΑΒΓ δΔ
You can find almost any symbol represented by Unicode through Unicode charts, like this one. A more accessible chart may be this one.
∫ ∬ ∭ ∮ ∯ ∂ ∃ ∞ ∀
