There are already a few version of the companion cube out there on craftster, but I wanted to share my own interpretation with you!
So, I started hanging out with my current boyfriend in June of 2009, and one of the first times we hung out after deciding to start dating, he showed me the game Portal, which has a "weighted companion cube" as the main tool.
Shortly after, he told me how (I believe) the makers of the game had made a real life version of the cube, but it was no longer available. That was when I decided I was going to make it, but I knew it had to be for a special occasion (as you can see, it's enough work to qualify for that a requirement!).
I drew up a plan for the cube, and put it in my pocket. I forgot it was there, and he happened to find it and said "what's this?" but I yanked it away and hid it before he could get a good look.
I decided I was going to make the cube for his birthday (and decided this about a week before it...his birthday is October 13th), and like most projects, I didn't make the cut. I bought a toaster for him instead, and decided the cube would be good for Christmas.
Between his birthday and Christmas he let me know that he had seen what was on the afore mentioned sheet of paper. I wanted it to be a surprise, so I put off completing the cube so he would either forget about it, or think I had decided not to make it.
Fast forward to February...I decided to finally finish the cube for Valentine's Day. As usual, I procrastinated and it got to be the week before VDay. Luckily, (but not for him) my boyfriend came down with a cold and had to stay home for the Tuesday and Wednesday before VDay (days we'd most likely have spent together otherwise). In that time, I finished the cube and a bit of lingerie...
Needless to say, my boyfriend was SO excited when he saw it. I brought it out in one of those bags you'd put a kid's bike or some other large toy in and he had NO IDEA what it was until he opened it. He looked just like a kid on Christmas morning and before 5 minutes had passed, he had taken a picture of it on his phone and posted the picture on Facebook. Yay for gift success!
I made the cube with felt (not wool felt, just manmade yardage from JoAnn) and decided it wouldn't withstand being stuffed very easily, so I sewed duck cloth to the back of each piece. I then stuffed it with 3 bags of fiberfill (and it could use more!) and handsewed the last edge shut. It's very generously sized - 18" cubed!
Thar she be: