Don't over-edit the vocabulary in the letter or try to get too clever with phrasing. You want to communicate that you can write, so make sure the letter is grammatically correct and well written, but if you find yourself going to the thesaurus to find "the right word" you're taking it too far.

Keep it simple, be polite and use proper grammar and you'll be fine.

I think the biggest advice I would lend to you, is get creative. I can't tell you the number of boring white and black resumes I've seen. The tech industry is littered with boring "business type" resumes and cover letters. If you truly want a job with a technology company, research some of the fun technologies out there and use them for your application.

Having a link to a youtube video, a twitter account, github (of what you do know), a cool presentation using sliderocket, etc..

These are the types of things that can set you apart from every other resume that the recruiter is going to find. Finding ways to get acquainted with tech professionals by showing up to meetups they go to. Use LinkedIn as your tool, it is amazing how much information you can find out using the internet!

It's about being proactive and not reactive! I hope this helps some.

I've been thinking about putting something together on sliderocket and then getting a hold of emails of the founders of the companies and sending it to them or something like that.

I think that would be a good approach, it also might be wise to see if you can find development managers or something below the founders. Depending on the types and sizes of the companies the founders may not be the best person to reach out to. See if the company has any HR on their payroll, once again a simple LinkedIn search can dig that up for you.

The important thing to remember is to be persistent, but don't be annoying. It's a fine line, and you'll have to realize when you're crossing that threshold. ;)

Don't get excessively wordy, but otherwise ignore the fear of sounding like a "business type". You're applying for a business role; if you were applying for a tech role would you be asking how to not sound like a "technical type"?

The application process is just a filter, especially at the intern level. Do what you need to do (ethically) to pass the filter and then worry about performing well in the internship.