I have tried to keep up my fitness by regular training for some years now, so I thought I'd share my current routine.
I tend to do 2 or 3 resistance/ bodyweigth training sessions per week. Usually I just do a full body routine, picking an exercise from each of the following: pull, push, lower body, core. To avoid eventual boredom and keep things fresh, I switch the routine with new exercises every 4 weeks. Also to keep up variety, I either do the exercises in a circuit fashion, or in supersets. Or a mixture of the both.
In a circuit one would perform all of the desired exercises in one continuum, without a rest in between the sets. The rest period would come at the end of the last exercise, before starting the next ”circuit”.
With a superset one would pair 2 ”opposing” exercises not using the same major muscle groups (e.g. pull/ push or lower body/pull, etc.). For example you would do a set of inverted rows, rest, do a set of push ups, rest, and repeat for the desired amount of total sets, before moving on to the next bout of exercises, be they another superset/ circuit/ singular exercises, etc.
I have understood that a good goal would be to with each successive week to increase the ”load” (more repetitions in an exercise/ reduced rest period/ added weight/ added set... ) to achieve advancement in your fitness. During the 4 week block you however should aim to have a ”de-load” week (either the 3rd or 4th week), where the repetitions and sets would be decreased. This way you would recuperate and recover sufficiently, and not burn yourself out with constant loading.
I also find it to be great to sometimes take some time of from the training totally and just concentrate on walking, stretching, mobility drills, etc.
During the summers I have the habit of cycling and hiking, and during winter to do some cross country skiing. Nothing like the great outdoors. :)
It is very interesting, that as people nowadays tend to sit excessive amounts of time, the posterior chain (glutes, hamstrings, back) appears to weaken and the muscles in the front of the body (hip flexors, pectorals, etc.) ”tighten up”.
Hence to balance things out with resistance training, it seems it would be a good idea to aim for more horizontal pulling vs. pushing exercises, and with lower body to put emphasis in doing more posterior chain exercises vs. ”quad-dominant”, ”anterior” exercises.
(In my previous training I totally missed the importance of balanced training, especially when it came to pulling/ pushing exercises. With all pushing exercises the humeral head of the shoulder is in an internally rotated position, as it tends to be in everyday, sitting activities as well. There is internal rotation of the shoulder present in vertical pulling exercises too, and if you do not incorporate enough horizontal pulling volume in your training, there will be be problems with your shoulders eventually.)
There is some good information on the subject out there, for example:
http://www.youtube.com/watch?v=pxbmcPzMKkI
Personally I aim to do stuff that can be performed at home, so I have purchased a selection of resistance bands (with an attachable handle), ideal for performing a plethora of pulling exercises. With gymnastic rings and/or ”TRX” -set one can do plenty of bodyweight pulling exercises (numerous inverted row variations, pull ups/ chin ups, etc.) as well. Throw a set of adjustable dumbbells in there and you are pretty much covered with all the pulling, pushing (there’s easily at least a dozen doable push-up variations and if paired with dumbbell pressing variations, one has a volume of pushing exercises to choose from) and lower body exercises.
When it comes to commercial gyms and the machines they harbor, it looks like most of them are actually useless and possibly even dangerous in the long run (excluding the cable pulley machines).
From
http://coretraining101.com/exercise-machines-suck/
1.) Exercise machines are NOT an optimal form of exercise for most. Exercise machines are great for isolating specific muscles (i.e. – the standard leg extension machine for the quads), but because exercise machines are anchored to the ground, your stabilizer muscles (muscle that surround your joints and protect them from injury), do NOT get developed. Exercise machines do not allow you to stabilize the weight you are lifting in three dimensions, and since daily activities such as work and athletics do require you to use these important muscles (the stabilizers), exercise machines are an inferior method of exercise
I haven’t seen the "foam roller" mentioned here on the forum, so I thought I’d bring it up here, as it’s a great and cheap device that can be used for ”self massage”. For people who sit a lot in front of the computer, especially the ”thoracic extension” movement and "rolling" the upper back could probably be of benefit:
http://www.youtube.com/watch?v=uzWOECAhsAM
http://www.youtube.com/watch?v=efbP1XdJ1fE
Personally I tend to break my sessions at the computer with foam rolling the upper back, doing thracic extensions and performing some light resistance, standing inverted rows every now and then. Really helps to keep the spine stay in order. :)
More on foam rollers:
http://sportsmedicine.about.com/od/flexibilityandstretching/ss/FoamRoller.htm
http://www.youtube.com/watch?v=8caF1Keg2XU&feature=player_embedded
Iron said:
Usually the people who advocate kettlebells says that, but there is no difference. I recall at least two studies that compared kettlebells with other modalities like dumbells or bars, and found no diference in gain of strength.
There is an interesting article here about the overhyping of kettlebells:
http://skinnybulkup.com/kettlebells-are-inferior-to-dumbbells
I guess they have their use in some movements, but hardly are not the be all end all of fitness. Perhaps the best way to train would be to pick the best of ”both” worlds (bodyweight, weights/bands/cable pulleys) and combine a suitable approach for oneself.
Recent article on Sott mentioned the dangers of yoga:
http://www.sott.net/articles/show/239981-How-Yoga-Can-Wreck-Your-Body
Especially the emphasis placed on the over extension of the lumbar back seems to cause havoc:
From
http://thefitcast.com/yoga-this-and-pilates-that
They don’t differentiate between good and bad range of motion. That is, these disciplines look at being limber as being healthy. This assumption couldn’t be further from the truth.
The truth of the matter is that certain joints in our body – the ankles, hips, and thoracic spine for instance – require more MOBILITY training because they’re too stable/tight. Conversely, some joints – most notably the lumbar spine and glenohumeral (shoulder) joint – require a lot more stability training because they’re too mobile. Every joint in our body is designed to function with a delicate balance of mobility and stability; some just need more of one than the other.
My main concern with yoga and Pilates is the tremendous amount of lumbar hyperextension that occurs; this is the LAST thing you want at the lumbar spine. Most back problems are extension-based; that is, people get excessive ROM at their lumbar spine because they lack ROM at their hips, or they’re just too weak to prevent it at the lumbar spine
More on Yoga:
http://www.coreperformance.com/daily/the-performance-life/5-questions-for-yoga-lovers.html
http://www.tonygentilcore.com/blog/reason-i-think-yoga-mostly-sucks-infinity/
...). Also I am not interested in gaining big muscles so I train with weights rarely, I am using a wide range of regular gym equipment just to fill gaps while exercising my abdominal muscles. So my workout is high in pace and I sweat a LOT so I am aware that I'm loosing some essential minerals & co but refused to use some suspicious supplements from fitness shops... 
