wow - loving the blackboard paint idea, DD has basically used the entire downstairs of our house as a giant canvas - i quite like to have obscure little alien creatures in multi coloured felt tip as my decor
DD is 2.3 and i do find entertaining her hard work. I too go to a toddler group pretty much every day, its great because each ones is different and there is always something different to do. My DD just loves to "make" which basically is eitehr, painting, cutting and sticking, and general crafty things. Its quite demanding of my time though, which is OK but sometimes it can be a bit much. Dont beat yourself up over the TV thing, if she wants to watch it, let her - i find that i just have the telly on ad lib, DD is not that interested now. I think if it is rationed the novelty doesnt wear off. Play dough is good too, you can make your own, plenty of easy recipes about andi prefer the home made stuff to the manufactured stuff.
If you live in the country you could go and collect leaves, acorns, conkers etc and then bring them home and "make" something with it. 18m might be a little young but she will enjoy "helping". So, thats two activities for the price of one
I love to patrol the charity shops around here (there are loads) and find lots of cheapo toys and books and DD is learning to spot a bargain as well. So that is good for both of us.
Duplo bricks are good too.
The thing i find frustrating is, the short attention span, you can spend ages getting something ready to "make" and then they play for five minutes and want to do something else.
I also rotate the toys, put some away for a bit and when they come out again, its like having new ones all over again