I'm in the same boat as you - used to be a hardgainer (still am) and struggle to put on any weight. I used to weigh around 78-80kg at my peak and was still pushing a decent weight, however this time around when i did my bulking cycle I've now gone up to 91kg and still got another 6wks of bulking left. I'm a massive fan of USN Muscle Fuel Anabolic when bulking but not for cutting. I use it post-workout and for my pre-workout I'm using Kre-Alkalyn with BCAA's. Also take a serving of BCAA's after training and glutamine and creatine and then ZMA before bed. I'm munching down around 4000 calories a day! I've put on some fat, but there's a lot more muscle and strength than ever before now as well.
Breakfast:
Big bowl of porridge plus 2 pop tarts and a protein shake
Couple of hours later:
Tub of cottage cheese and a croissant with nutella and peanut butter
Lunch:
I get these ready meals from www.musclefood.com or 2 chicken breasts and brown rice, then yogurt and something sweet
Couple of hours later:
Fresh fruit (just a random mix of anything)
Oat/cereal bar
Pre-gym:
Pasta with tuna, or salad consisting of avocado, peppers, mozarella and tuna
Post-gym:
USN Muscle Fuel Anabolic
Dinner:
Anything high in protein and carbs
My training is a four day split:
Monday - Legs - Squats, Leg press, Hamstring curl, Lunges, Calf raises
Tuesday - Chest - Incline bench, Flat bench, Flat flyes, Cable flyes with handles at the top, Machine incline press
Thursday - Back - Bent over barbell rows, T-bar rows, Single arm dumbell rows, Wide grip lat pulldowns, Narrow grip lat pulldowns
Friday - Shoulder & Arms - Military press, Arnie press, lateral raise, Reverse flyes (rear delts), Shrugs, Barbell curl, Skull crushers, Superset hammers with dumbell tricep raise, superset preacher curl with tricep cable pulldown
The training routine I use for the big lifts is Jim Wendler's 531 Routine. You may think you're not doing many reps, but try it out for a few months. My strength went through the roof and I found myself putting on a kilo a week in mass! But key thing for weight gain is YOU GOTTTA EAT
Give me a shout if you need any info mate