Write a generic cover letter that just requires you to fill in the blanks for whatever job you are looking at. Short and sweet is best!

I use something along these lines:

Hi,

I would like to apply for the <<job title>> position which was advertised in <<where you saw the listing>>. As you can see from my attached resume, I have extensive experience in <<bullet point from their job ad>> due to the time I spent <<doing whatever it is that is relevant>>. Additionally, I <<another impressive thing you have done that is relevant to the job>>.

I'm passionate about <<bullet point form their job ad>> and would love to meet to discuss why I'm the perfect fit for this position. You can reach me at <<phone number>> or this email address.