The key to any weight gain, whether you're vegan like us or not, is to take in more calories than you can burn. No supplement, powder or vitamin will allow you to put on weight unless you are exceeding your body's caloric needs.
The easiest way to gain weight is to start a food log. You can do this online at nutridiary.com or a similar site. Record what you eat for a week, and then add 500 calories per day to that, and you'll gain weight at the rate of roughly one pound per week.
Unless you're training hard, protein powders and creatine (FYI, creatine monohydrate is the only vegan form of creatine) aren't going to do much. Protein helps repair muscle damage, and creatine improves muscle endurance. Neither of these are a magic-pill, and they both require you to eat the right amount of food.
Someone already linked Vega, which is essentially a protein/nutrient powder for making shakes. Vega was designed by
Brendan Brazier, a vegan professional athlete. I've met Brendan in person, and while he's not a very big guy at all, he's a very powerful man. He's also written a book. I'd suggest Vega more for people who are already pleased with their size and are looking to get into better shape.
Charlie is a raw vegan bodybuilder in Hawaii. He has a book available on his website in PDF form for $10. The book is a great investment. He also has information on his website including what and how much he eats; he eats nearly 3600 calories a day, but only around 80 grams of protein.
There's also
Vegan Bodybuilding and Fitness, which is an online community for vegan bodybuilding, including dietary info.
The biggest thing to take away from all this is: you are what you eat. If you want to get big, you have to eat big.
