Here is a list of the tools I use to make jeans.
The Sewing Machine
The most important thing about your sewing machine is that it is made for sewing thick fabric. I use this Kenmore sewing machine. It was their cheapest model when we purchased it, so you don't need anything special. It said on the box that it works well with denim, and it does. It's also important that the foot can lift up high enough. When making jeans you sometimes run into some very thick parts to sew through.
The Needle
It is important to use a heavy duty needle when sewing denim. As a general rule thicker fabric requires a thicker needle and thinner fabric requires a thinner needle. If your needle is too thin it will break. If your needle is too thick for your fabric it can tear holes in it.
The Feet
The first foot is for making automatic button holes. I don't always have a spare button to get the size of the holes right, so I sometimes use a coin. If you have an older machine that doesn't make automatic button holes you can make them with two rows of tight zigzag stitches, then simply reinforce the ends with a wider zigzag stitch.
The second foot is the basic A foot. This is the one you'll use for most stitches.
The third foot is for an over-the-edge stitch. If you don't have a surger you should use this foot on the outside of your seams so they don't fray. If you do have a surger it still comes in handy for more precise sewing, or sewing small pieces.
The fourth foot is the zipper foot. This simply enables you to get close to the zipper without it getting in the way when you are sewing it on or reinforcing seams around it.
Basic Sewing Tools
Like every sewing project you will need a pair of good sharp sewing scissors. When cutting denim this is especially important because denim is thicker than most fabrics. You may want to have a large pair of scissors for long cuts and a smaller pair of scissors for more detailed cuts. A set of good pins is also a must. My lovely wife and I highly recommend a magnetic pin cushion which makes removing pins and recushioning them a snap. If you want your seams to line up right, I have yet to find a good substitute for pinning the fabric in place (I tried masking tape once; it worked okay, but was a little messy to remove). Fabric pics are also a must. It is difficult to sew an entire pair of jeans without ever making a mistake. A ruler, a good measuring tape and something to mark with always come in handy as well. I use washable markers, but I hear chalk and white soap also work well.
A Surger
I got this Singer surger on sale for my wife as a Christmas present. It turns out I use it more than she does. There's nothing special about this particular model; it was the least expensive one I could find with a good brand name. I use the surger primarily for doing the initial stitching of most of the seams. As a general rule if the edge of the seam is exposed then you should use either a surger or an over-the-edge stitch. If you have a surger it will save you a lot of time and your seams will look more professional when you turn your pants inside out, but if you don't have one you won't see the inside seams when you're wearing them anyway.
