Phil,
I can speak from a little experience and from a lot of research. The first thing you should look at is whether or not there are any requirements or restrictions for the porfolios. Some will give you a maxiumum size, number of works, they might require you to send slides instead, and many other things. Off the top of my head I would say mounted work would be unacceptable. However, almost all the research into porfolios I have done were for architectural portfolios. For the few M.F.A. in photography programs I looked at, I believe all asked for a set of slides.
I think the most important advice anyone can give you is to start early. It looks like you're doing that because as far as I know most programs have deadlines in December or January, but I'm unsure of how many admit students in the middle of the year.
Also, I am assuming that you intend to apply to a shool nearby, but if you are willng to move, you might want to look up information of the faculty of the programs, and whether or not you would want to work with them. You should usually chose a school based on its faculty, rather than its name.
My personal experience is that my work was way too traditional for any program. My work has more in common with Eugene Atget and Ansel Adams than Robert Parka-Harrison (whose work I do like) and Joel Peter-Witkins (I might have spelled his name wrong). Every program I looked into wants that sort of "modern" and "edgy" look. I talked to a number of professors about my work and most did agree that it probably wouldn't get me into the program, which I decided was O.K. beacuse my goal is to be an architect and to just keep doing photography on my own.
I tell you this in case your work is the same. If your work is a bit on the traditional side too, then it might be harder for you to get in, though it certainly isn't impossible. Also keep in mind that everything I just said applies to graduate programs, I'm not sure how undergraduate programs work because I was in an undergraduate program and I wasn't looking for a second bachelor's degree.
Also, my last bit of advice- I promise! Most (maybe all) photography professors say it's more important to show your style and for all the work to fit together, than to show versatility in all sorts of areas. Some professors say to even construct the portfolio so that the entire set fits together, like one long series. I chose for my work to all fit together, but it's not meant to be a long series (because I usually don't work like that) but rather I had a couple of paired photographs that went together, along with other work since I was applying for an architecture program (for people with no experience in architecture, hence the photographs). Of course, I have only heard back from one school out of five so I'm not sure how successful my idea was.
On a side note, since you've been away from college for a while, or at least I assume you have been since you say you're considering returning to college, you should have the opportunity to talk about what you have been doing since college, which could help you and make up for what you say is your scholastic failure (remember no one is a failure!)