At that age we read books until I was hoarse and then read some more. There is one called Peek-A-Moo that was a favorite, it has extra large flaps that are easy for beginning flap-openers, to begin with I would hold the flap slightly open he would just kind of rake it all the way open to reveal an animal saying moo or cockadoodledoo.
At the library if you haven't yet found the children's song/story hours inquire, it was great to have something to go to. A Kindermusik or other music-exposure class or a Little Gym movement class can be fun at this age also.
A big (shallow) pan/bowl/tub of water on a towel on the floor, the lets see what floats game. Its like bath toys, but because its on the floor it is new and different, at least the first time

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Children's keyboard, not the baby type but a child's one, surprisingly cheap at Target/Walmart.
Other things we had were a bouncer/exersaucer and a walker (yes the media says dangerous -- but only if its at the top of stairs). About this time we also bought a toddler swing (the outdoor type, a enclosed seat with ropes to hang on a swingset) and instead hung it from hooks put up into a sturdy door frame inside the house, allowing for at-home real swinging, that was a big success especially as all winter was too cold for the playground.
Maybe about this age DS first enjoyed having me make a house/cave from a sheet over some chairs, we would sit inside and read books or have a "picnic".
Bubbles if you haven't played with them before. My DS did not see what the big deal was about bubbles but most kids really like them. They have bubble machines that operate on a push the button out comes bubbles principle, which is great for kids too young to blow, I was always looking for things that gave DS a sense of being in charge of making something happen.
Visit a pet store especially one with a big tropical fish section. Or an aquarium is even better, if you live on the coast. If your DS likes things moving/waving like in the wind he will probably enjoy watching and learning about fish.
This was a difficult age for us as DS was really wanting to do things but physically still trapped. He did not crawl either. He didn't much like toys, preferring to be interacted with in some mentally stimulating waylike constantly shown things. I was at my wit's end by 10 am a lot of days.
Polly