[Dogxzysl]

I say split your resume into two different one.
One where you ignore the jobs that you only list for a few months. When I see multiple jobs of short duration, I consider it a big red flag (similar to gribbler's comment) This one could be used for those low end jobs. Once you've taken those out, those left show you're willing to put in some time. Then you can say that you finally left those places because you didn't see the long term potential. So you went someone else to start at the bottom and work your way up. You're qualified (education wise) to work your way up. And that's why people will hire you for an entry level position even when you appear over qualified.

Your other resume will only be used if you're applying for a position at a financial company where having that experience might actually benefit you. When asked why so short, say the economy and layoffs. Contrary to what Zoetstofzoetje posted, due to legal issues, almost all decent sized companies in the US will not say squat about a previous employee except to acknowledge that they did indeed work there. Some companies are not even verifying employment dates (but most still will). Our company sent out a note warning people to not even provide personal recommendations on previous employeeds.

And yeah, do a specific cover letter for each job. As suggested, do a little research about the company so you can tailor your cover letter better. Always state that you believe you have the skills that will benefit the company over the long haul and that whatever the job you're looking for, will lead the the career that you've always wanted.