I'd say, leave education off, and go with functional, like ehBeth said. Particularly for an IT resume, the employer wants to know things like, what languages do you know how to program in? How extensive is your knowledge of HTML? etc. So GED or standard HS diploma doesn't matter to them.
I use either Sincerely, or Very Truly Yours, (a standard lawyer's construction) at the end of cover letters. I make sure to put my contact info in and something about I look forward to discussing this opportunity with you. And then follow up with a phone call in a week or so - that can be very impressive, as it shows you're not just sending letters out to the void, like a lot of people do. Employers realize they are being mass-mailed to, but they don't want to feel that that's the case with you. So personalize as much as you can; that takes away the mass mailing feel that a lot of these things have.
And - spit back to them (that's an icky metaphor, but you know what I mean) what they said in the ad or what you've read in articles about the company, and use that as the body of your cover letter, e. g.
* the job says they want data migration. Tell them how you did data migration for such and such, used these types of tools, delivered the end product on time, under budget, etc., that type of thing.
* a recent article about the company (or, better yet, about the person you're writing to!) mentioned they're changing over from WordPerfect to Word. Tell them how long you've worked with Word, the kinds of things you can do with it and how you can help train people and assist with the transition.
* the company's website says they have a philosophy of taking a chance on new talent. Tell them what kind of a sure thing you are; make them believe that you're a good chance for them to take.
You get the idea. Currently, I have my resume in to a place where the cover letter is extremely important and is reviewed as closely as the resume. I started my cover letter to them with a sentence something like "I know you're going to get a lot of applications for the position of __, all promising different things. However, I'd like to show you how I can handle the job of ___ for lower costs." Argh, it was something like that - the idea was to tell them that others may say they have the skills, but I can bring it to you for less (this is a place that I believe is rather budget-conscious). This all translated into an interview and a strong possibility of a second interview.
Finally, one way to find out what's important to a company is to ask - not necessarily the interviewer, but the first line of reception might be able to help you in general ways, e. g. a cover letter isn't important, or they just had layoffs or the like. Look at company websites and scuttlebutt websites like
www.vault.com for insider info, but be aware that scuttlebutt websites often contain a lot of bitter people, so read everything there with a critical eye.