If you simply just had the TV on a lot as background noise, you can play books on tape (free ones can be sound, like at LibriVox) or music (either CDs, playlists or even Pandora).
Long baths and long walks are always nice space fillers. You can always do walks around other places when it's cold (although walks in the cold are quite nice! But once it gets below like 12, it's nippy)--the mall or the Y or the track at the local school or church. Sometimes even just getting out and hanging out at the bookstore can be fun.
Also, bubbles, art projects, making playdough, playing with water and different textures, I agree with lights--flashlights, finger puppets, always good times. If you have a sand/water table, that can be quick entertaining.
I always set up later afternoon playdates, which was useful as a distractor.
You could set up forts and tunnels in your living room. Also, since your son is at an exploratory stage you could set up the area with things for him to get into that are considered acceptable. I used to set my kid up with a bag of stuff so he could dig through it and find new things.
So that I could knit or sew, I would give my son paper with a big, blunt needle and yarn and let him sew himself. Or lacing cards provide a similar experience. Those used to entertain him so I could work on some craft for a bit.
I agree that while it's an adjustment, you will adjust and you will begin to find a lot to do. The age your son at is a hard age--all they want to do is explore (with their hands, feet and mouths!). But soon that stage will pass, and you will find it easier to fill the time.