The best results come from hard work, dedication, and a good bulking diet. Supplements are really not worth investing in, although if I had to recommend one it would be whey protein
http://www.wheyconsortium.co.uk/
these people are very good. Aim for 1.5 grms protein/lb of bodyweight.
If you were serious you can legally obtain pro-hormones such as tribulus but I would think long and hard - they are expensive and the results are sometimes not worth the price paid.
Anyway, remember that Rome was not built in a day, and neither will your body be.