I'm looking to change my workout, just to keep me motivated (I do this every 3-4 months) and wondered if there were any home gym/free (open source like) programs similar to Crossfit or p90x. The problem with either is that they require specific equipment or dvd's......and I'd rather not pay anything.
CrossFit is a free program. It's completely "open source" insofar as the exercises are published and free to use without charge. You just can't slap CrossFit logos on everything and try to make money off of it without becoming an affiliate.
You can do a great many CrossFit style workouts with bodyweight alone. Some ideas include:
With very minimal equipment you can add even more exercises. Since you mention home gym I'm going to assume that a set of dumbbells is a given:
If your home gym has even a single barbell that opens up a ton more exercises. If you don't have bumper plates you'll just have to avoid max overhead weights.
If you're willing to spend minimal money you can add several more CF exercises to your repertoire:
The only thing that's noticeably lacking is pullup equipment. You're stuck with either buying a bar, or you could spend $30 and get one that fits in a door frame: Iron Gym Total Upper Body Workout Bar. I have one of these and it works great for pullups. Unless you're really short you won't be able to do kipping or butterfly pullups, just deadhangs.
Join a Meetup group
You don't need a program, you need people already doing it to join with.
To stay motivated during a high intense workouts you'll need other people do to it with. It's free and unless you live in the styx you should be able to find a P90X or equivalent fitness group near you.
From my personal experiences with meetup doing other activities (snowboarding, wakeboarding, etc) the people are generally very helpful/accepting as long as you don't act like a complete douchebag.
Chances are, you'll probably find a group with a core of members who are super-active and at a much higher level than you that will have tips/pointers to help get you through the plateaus.
If you're really dedicated to stepping up your progress in the long term it'd be best to accept that this is something that you want to do as a lifestyle, not just a hobby.
The workout regiment programs are only really useful as a crutch to get started. It sounds like you're beyond that point and starting to settle into the maintenance/plateau stage.
Personally, when I plateau during a workout I lay off of the workouts for a few months before I start again because I have other activities (extreme sports mostly) I do to stay in shape. Ie, I don't really exercise as a lifestyle so the extra effort isn't 'worth it' but fitness isn't my primary goal.
I'd add a few things to hobodave's response: