Exercise at home for beginners with 100lbs to lose?

I'd recommend Leslie Sansone's Walk Away the Pounds

This is your basic 5 x 5 template. (To clarify, 5x5 is 5 reps x 5 sets. The idea is to work at a difficulty level where you could only do maybe 7-8 reps on the first set, and are struggling to finish 5 reps on the last set). You would do strength training 3 times a week, say Monday-Wednesday-Friday with the weekends off. These are done "lazy circuits" style, with about 1 minute rest between each set. The explanations of the exercises you'll use for each group are farther below.

Workout A
1A. Knee dominant - 5 x 5
1B. Horizontal push - 5 x 5
1C. Horizontal pull - 5 x 5
2A. Ab - flexion - 3 x 5
2B. Ab - static 3 x 30 seconds

Workout B
1A. Knee dominant - 5 x 5
1B. Vertical push - 5 x 5
1C. Hip dominant - 5 x 5
1D. Vertical pull - 5 x 5
2A. Ab - rotation - 3 x 5
2B. Grip and neck training - 3 x varies

Exercise Progressions - with regular weight training you can just add weight to the bar. With bodyweight progression is mostly about changing your leverage. These are just a few examples, I could come up with dozens more if needed. Google is your friend if you are unsure what an exercise is or how to perform it properly. Youtube is usually a good resource. Remember also, you can always add resistance in the form of a weighted vest, backpack, or resistance bands if necessary.

Explanations of exercise in order of difficulty (easy-hard)
1. Knee Dominant -- squats, lunges, step-ups, bulgarian split squats, unilateral bent leg deadlift, partial one leg squat, one leg squat, box or stair pistols, full pistols.
2. Horizontal Push -- pushups, decline pushups, resistance pushups, side to side pushups, stair one arm pushups, negative one arm pushups, full one arm pushups.
3. Horizontal Pull -- body row, resistance body row, negative one hand row, incline one hand row, full one hand row.
4. Ab - flexion -- crunches, situps, resistance or incline situps, reverse situp, resistance or incline reverse situps, hanging knee or leg raise, hanging pikes, rollout from knees, rollout from feet, dragon flag. Also included are oblique moves like side lying crunches with or without resistance and side lying two leg raise.
5. Abs- static -- 4 point prone bridge, 3 point prone bridge, 2 point prone bridge, 4 point supine bridge, 3 point supine bridge.
6. Vertical Push -- pike pushup, hindu pushup, divebomber pushup, decline pike pushup, decline hindu pushup, decline divebomber pushup, one arm pike pushup, negative handstand pushup, handstand pushup with head touching floor, full handstand pushup.
7. Hip Dominant -- supine hip extension, good morning, one leg stiff leg deadlift, split one leg good morning, one leg supine hip extension, hyperextension, one leg hyperextension, natural glute-ham raise.
8. Vertical Pull -- jumping or assisted pullups, pullups, resistance pullups, side to side pullups, negative one hand pullups, one hand pullups. All these can refer to chinups or neutral grip pullups as well.
9. Ab - rotation -- twist crunches or situps, resistance or incline twist crunches or situps, russian twists, lying windshield wipers, standing rope rotations, hanging windshield wipers.
10. Grip and Neck Training -- for grip you can use handgrippers, deadhangs from a pullup bar (especially a fatbar or gripping a towel). For neck nothing beats wrestlers bridges. If you are involved in a striking martial art or sport, finger and fist pushups are very important also.

None of these lists have to end here. If you get strong enough you can always add resistance to your full range of motion one limb exercise. Or if you can do more than 5 one hand pushups do decline one hand pushups, or start working on one hand hindu and then eventually one hand dive bombers, and so on.

The nice thing about this routine is it scales dramatically depending on your fitness level. If you can't do even ONE regular pull up, you can scale it down and do assisted pull ups (legs on a chair), or ballistic pullups (where you jump to provide the initial momentum). It's actually easier to do properly when you're very unfit...because once you're healthy and strong...you're going to be searching for challenging enough exercises to only allow you 5 reps max by the finish of the 5 sets.

If you need any help with choosing exercises, or anything else, let me know!

I'd recommend Leslie Sansone's Walk Away the Pounds

Just to update, for the first time I tried Leslie Sansone's 1 Mile Walk on youtube today and I'll definitely be doing it again. Its at just the right level - thanks ever so much to all those who suggested it.

I'll also definitely be revisiting this thread in the future, to look at other exercises to try.