The weight-stack machines are fairly useless for the purposes you are looking for, free weights are the best way to go. There are some useful bits of kit knocking around most gyms though and these are:
T-bar rower: if you can't make the base-weight for barbell rows then this is the next best thing, but is no replacement for barbell rows. The only problem with the real thing is that to rack up the barbell you immediately need to be able to pull 40kg (i.e. 2 x 10kg plates as a minimum, plus the bar). So if you can't do 40kg with good form you could start using this machine (though it has less range of motion), but as soon as you can do barbell rows switch to them.
Hyperextension bench: I absolutely LOVE hyperextensions, they really blast your spinal erectors. I do 3 sets as a warm-up on my back day.
Smith machine: it's a machine at the end of the day even though you load on 'real' plates, so no replacement for barbell or dumbell bench presses but if you don't have someone to spot for you they are a good alternative. I've had excellent results from smith bench presses in the past.
The leg press is my friend at the moment. I got a spine injury almost a year ago and so couldn't do squats. These got my legs working without putting too much weight on my back so were fantastic. But don't be fooled by the amount of weight you can press: it's artificially high. At the moment for example I can press nearly double what I can squat. But now I'm getting back into the squats because quite simply, they rule: 3 sets of squats, 4 sets leg press, 2-3 sets calf raise (I use the sitting calf raise machine for this- personally speaking I don't know of a free-weight based exercise specifically for calves that allows me to push decent weights so this is my best option)
Then you have the various pulleys: tricep pulldowns, cable rows, lat pull downs - all decent exercises, but deadlifts, pull-ups and barbell rows (for back) and skull crushers (triceps) are IMHO better exercises - it's a personal choice in many cases though.
The machines to completely avoid are:
- Bench press machines (in any of it's forms: sitting, lying, incline, etc)
- Dip machine (IMO the biggest waste of time of them all)
- Assisted pull-ups (ask someone to hold your legs whilst you do the real thing instead)
- Pec deck (puts your shoulders and back at weird angles, plus I have NEVER been able to shift decent weight with them vs. dumbell flyes)
- Preacher curl machine (it seems to work my shoulders, not my biceps!)
- There was a weird crunch-machine in my old gym which always seemed to have a queue for it, which was great because it left the decline sit up bench free
