Jimski, your reasons for weight training almost exactly mirror mine! In college I was also trying to bulk up, and gained 25 pounds in one year, going from 165 to 190. Now, two years out of school, I exercise to get my happy endorphins, to be able to eat what I want (I love food), and to do similar "dad" duties. I won't be a father for a number of years yet, most likely, but it comes in super handy when my girlfriend wants to rearrange furniture in our living room, or carrying our bags on vacation

.
When I started getting into bodyweight exercises about a year ago, I googled "bodyweight exercises" and just started flipping through all of the youtube vids and links that popped up. I already had most of the equipment necessary: my own body, a couple of stools to do dips on, and a couple of dumbbells and an EZ curl bar in case I wanted to change things up. For a pull-up bar (very necessary) I went to Bed, Bath, & Beyond and picked up an "Iron Gym" pull-up bar for $25 ($30 minus the 20% discount coupons they always send in the mail). It's rated for 300lb, but the metal will give a little bit anyway. Don't worry too much...I'm at 185lb now and since the initial "settling" of the metal bars it's been fantastic. If you have some strong piping near your house, you won't even need to buy a bar.
I started with the standard push-ups, pull-ups, curls, sit-ups, dips, etc., but those, honestly enough, can get just as boring as lifting weights. So then I saw two things that I thought would really make the exercise more dynamic. First, parkour, or free running. Do a quick google search on that and you'll find a bunch of sites and videos of guys/girls doing parkour exercises. Modify them for your own home, and all of a sudden you're combining running and lifting that doesn't get old. A lot of these exercises, even at the beginner intensity I do them at, are pretty difficult. I'm *still* trying to do a clean muscle-up!
That stuff led me to gymnastics. Dan Gill, one of the developers here, is actually an accomplished gymnast, and he's pointed me in the direction of a few places where I might take adult gymnastics courses. In the meantime, before I start, I'm trying to do some planche pushups, , over-the-head pushups, wing pushups, handstand pushups, and various L-leg dips or horizontal pull-ups/curls. (It's like doing a pull-up, but instead turn your body so that your back is parallel to the ground, rather than perpendicular. Start off with your feet tucked and get used to that position. As you get better, start extending your legs. Your abs will hate you!)
This site seems to have a lot of gymastics exercises.
This one has some good ones, too.
Do a youtube search for prison workouts or ghetto workouts. Burpees seem like they'll kick my a$$!
In the past two months, I've stopped doing crunches and other ab-only exercises that flex your spine. First off, if you're working your stomach and not your back, you're creating an imbalanced core, and that could hurt you down the road. Secondly, that constant spine-flexing motion can eventually lead to a herniated disk

. No thanks. Read
this NYTimes post about it, and watch the video. Planks, dynamic planks, mountain climbers, all of those exercises will work your *entire * core, not just your abs. Much better.
Search for some
plyometric exercises. My own favorite is the split squat jump (good for skiing, too!) Just start those slow, as plyometrics can be intense. Really good for explosive muscle power and cardio, too.
Once you amass an arsenal of your favorite exercises, start changing them up. Try the
Tabata Protocol with a few of them (without weights). It's really intense, so start off doing a 20-second work/40 second rest ratio, and then start working down to the Protocol's 20:10 ratio. Another
Times article discusses some studies that are finding that short bursts of super-intense excercise have just as much cardio-vascular benefit as endurance exercises (like running, biking, etc.), and will help you build muscle power as well. So when you only have 10 minutes instead of your usual 60 to work out, you can do an intense interval workout and still benefit.
By far the most helpful thing I found in working out, however, was finding a full-body sport. I am a HUGE advocat of rock climbing now, and whenever I go I find that my entire body has been used. Plus, it's a really cool feeling to use your own body to scale a vertical wall, and done correctly, climbing has made me feel more limber, more aware of my body position, and has made me stronger.
I'm sure you could find something similar to climbing that would get you really excited. You've mentioned that you play tennis, and I'm sure that's pretty intense for almost your entire body (except your non-racket arm

). Free running might do it for you, or gymnastics, or martial arts, or just tooling around with the bodyweight exercises you find might be enough. What I really like about these kinds of workouts is that once you've learned, or had a bit of training, these are all sports that you can advance in and practice on your own. I would be interested in hearing if you end up finding something that you enjoy!
I'll try and scrounge up some more links later on. I know I have a whole bunch of bookmarks for bodyweight excercise sites somewhere...
Hope that helps!