I used folded newspaper tubes for my peas last year, and plan to do the same this year too.
I cut sheets of newspaper in half lengthwise, and fold about a third of it over (also lengthwise). I roll the paper around a spice/herb jar (Tesco sell their herbs in square jars which are perfect for maximising space) and fold the excess over at the bottom to form the base. Slip the jar out. I sharpen up the corners, but that's just me being a perfectionist and completely unnecessary.
The advantage is you can make them as deep as you like by using wider paper (or not folding it over so much) or bigger by using a larger "form", such as a deodorant can or something. The paper also costs me nothing as my boyfriend's dad gives me his papers once he's read them. (I also take a perverse delight in making something useful out of the Daily Mail, a paper that I utterly despise.)
The disadvantage is that they take time and effort to make, but I do them while I'm watching TV or listening to music or audiobooks when I wouldn't be doing anything else anyway. They also tend to break up a little at the bottom when you plant them. That's no big deal to me though, they are going in the soil at that point anyway.
