Here is my List of Weightlifting Accessories, separated into four categories: Useful, Sometimes Useful, Mostly Useless and Utterly Useless.
Very useful at protecting your hands from blisters. Some people might consider them unnecessary, but if you've ever had blisters on your hands from weight lifting you will agree they are a must have. They are also useful for gripping barbells easier.
The company I use is Atlas, but I also found a pair of bicycle gloves "Copper Canyon" that are practically identical to the Atlas weight lifting gloves.
#2. Dumbbells = Useful
You are weight lifting. You are going to need lots of different dumbbells in different weight sizes. This is an useful must have - unless you are trying to take the frugal exercising approach, in which case you will need to build your own dumbbells out of scrap.
#3. Wrist Wraps = Sometimes Useful
Wrist wraps provide extra support for your wrists, but not everyone needs them.
#4. Lifting Wraps = Mostly Useless
These are designed so you don't have to worry about your grip so much. You attach them to your wrists and then wrap them around the barbell you are lifting, making it easier to maintain your grip. However if you already use weight lifting gloves, then these things are pointless. I toss these in the Mostly Useless pile.
Are you deadlifting and feeling pain as you are lifting the weight off the ground? Then you probably should not be lifting that much weight in the first place. A deadlift bar jack holds the barbell slightly off the ground so you don't have to bend over as much (and strain your back). But if you look at the photo on the right you see it only raises it off the ground by 1 or 2 inches, so does it really make difference? No. Not by much. If your back is hurting you that much, then stop lifting so much at once.
#6. Dip Belt = Mostly Useless
Are you planning on holding weights between your legs while doing pull ups or similar exercises like the guy in the photo? Probably not. So this would only be useful if you actually plan on doing this. I was very tempted to put this in the Utterly Useless pile, but it does have 1 use.
#7. Gym Chalk = Useful
Lets pretend for a moment you don't like using gloves and you want more grip. Well gym chalk is the old fashioned solution. Gives you plenty of grip. Also available as 'chalk balls'.
Similar to the wrist wraps, lifting belts are designed so you don't throw your back out lifting something you should probably not be lifting in the first place. But sometimes people don't know their limits so it is wise to be wearing one of these if you are going to be lifting anything which will be using your back muscles a lot.
#9. Knee Supports = Sometimes Useful
Same deal as the wrist wraps and the lifting belt. If you are lifting heavy weights with your knees you may want to be wearing knee supports.
If your grip is really that bad, then you should get a set of lifting hooks. They work waaaaaaaaaaaay better than lifting wraps and you are guaranteed not to be dropping whatever you are lifting.
#11. Liquid Grip = Sometimes Useful
Conceptually, these work the same as gym chalk, but honestly I don't see this being a necessity for anyone who is not a full time bodybuilder. If you're just doing weightlifting for exercise, use gym chalk. If you are doing it 4 hours almost every day then okay, get the liquid grip.
#12. Head/Neck Harness = Utterly Useless
Seriously??? Are you going to be lifting things with your head/neck like the guy in the photo below? Unless you are then this is going in the Utterly Useless pile.