I started with Heinz rice porridge for 4 months +. It's like a powder form, I just mixed it with breastmilk or cooled boiled water and fed baby. The Heinz was for convenience sake as I wasn't sure how to make porridge for her age at that time. She got bored with it after 2 weeks, so I started introducing other foods - e.g. cooked and pureed vegetables like spinach, pumpkin. I also stopped the Heinz and started making my own rice porridge, to accompany the pureed vegetables. I also gave brown rice porridge. Now that my baby's 6 months +, I give her oats porridge for breakfast (the organic baby type, not adult instant oats type) that I bought from a health food store. Some people say that oats porridge is also ok as a first food.
There's also this website that I frequent for recipes: Vegetable Baby Food Purees, Easy & Yummy Vegetable Baby Food Recipes for Your Baby (this is the vegetable page, you can go to the main page and start browsing from there)