My son has been teething since he was three months old (and got his first tooth the day he turned five months), and these really helped him. They say you're not supposed to put them in the freezer, just the fridge, because they get too cold, but we put them in the freezer anyway. His teething pain was BAD, and the fridge just doesn't get them cold enough to help numb their a mouth a little. I am not a doctor by the way, this is just what I do.
Magic button
We call it Wes' "ipod," and it really is magic because it stops a baby's crying the second you push the button. It's actual name is Baby Einstein Take Along Tunes, but that doesn't give an accurate enough description. It's a little square box with a giant button in the middle, when the baby (or whoever) pushes it, it plays music and lights up. I swear by it, my sister-in-law swears by it, and I have a couple of friends who do too. It's also the #1 bestseller in the "baby musical toys" category. I don't know what it is about this toy, but it really is magic. He's one now and we still take it with us everywhere.
Saucer or jumper
We bought him the Baby Einstein Rhythm of The Reef Activity Saucer. He was obsessed with it from 4 months old until about nine months when he started walking. He was a little small for it at first, but I just folded up blankets and put them under his feet. It seemed like every week he would discover a new component to the thing, and it would keep him busy for about fifteen minutes at a time. Which is a long time! I would pop him in this while I was making dinner, or I would drag it in the bathroom so I could take a shower.
Books
I started reading to Wes a couple weeks after we got home from the hospital. He didn't pay much attention then, but he absolutely loves reading now. Sometime between 5 and 6 months he started turning the pages, around 11 months he started bringing me books to read (he was walking), and now he points at things in the book so I can tell him what they are. I can not even stress enough how important it is to read to your baby. Not to mention the fact that if you want to have a lazy day it's a great way to keep your baby busy. We once read every book he owns in one sitting.
Stuffed animal
His giraffe came everywhere with us for a long time. Sometimes it was the only thing that would calm him down in the car. It was his little snuggly security object. Now that he is old enough to sleep with a stuffy in his crib, we upgraded him to a stuffed lion he picked out himself. He still loves his giraffe though, so his giraffe is his carseat stuffy, and his lion is his crib stuffy.
Mesh food bags
These help so much with teething. Before he was eating solid food I would put frozen breastmilk in one. Now I use frozen peaches (his favorite). These things are also work well for getting them to eat fruits or vegetables before they have teeth and are able to chew. The holes in the mesh are just large enough to let the juice and smalls fibers through, but small enough that the kid doesn't choke down any large pieces. I think this is what they're actually made for, but I've mostly just used them to help ease teething pain.
Push walker
A couple days ago I was at the park with Wes, and a guy came up to me and asked how I "trained" him to start walking so young. I definitely don't train him to do anything, and I think kids learn to do things when they are physically and mentally ready. Some walk early like Wes, and others start walking later, but may be doing something else early. I don't there is anything wrong with a baby that starts walking a little later. I wish Wes could have stayed a cuddly little baby that wasn't getting into everything a little longer. Annnnyway, when he asked me that question the only thing I could think of that we did was give him this walker. Did it help him walk sooner? Who knows. He sure did love pushing it around for about 4 months though.