Of course for the development of strength, a solid weightlifting program is a must But when it comes to supplements what you first need is the proper product to amplify the results from your workouts.
As CS mentioned the best product to do that is PLAZMA which you take pre and during your strength workouts. This product will give the proper nutrients so that you can maximize performance, growth and repair. If you can train harder, recover faster and build more muscle it will be easier to gain strength.
Another proven product is Creatine which has been shown to increase strength via several factors.
It increase your capacity to perform during intrense efforts lasting 10-20 seconds (which is a zone where strength is trained)
It increase intra-muscular fluid retention which gives you better strength leverage
It increases satellite cell activation which facilitates muscle growth
It can reduce myostatin expression which will also help build muscle