We had a ball the other day doing feet painting - I literally covered the dining room with sheet paper and old carboard boxes and had two plates of paint and let him loose. I did make sure I had a bowl of hot water, a naked child and a towel first but I'm not currently houseproud as we are doing the house up - but he didn't make any mess.
Garden play still goes on here - including water play, sand play, and mud. We also do some gardening which he's really good at transferring compost and clearing stuff for me!
I've found a few good preschooler sites on the computer that DS quite likes but I restrict them to 15 min a day.
Cooking - DS joins in everything I cook.
We do quite a lot of painting, playdoh, sticking, scissor practice, whatever the latest craft thing I can think of.
Reading.
Cushion chaos/bouncing on my bed
Making a den
Duplo takes up loads of our day.
Washing up
Walks, puddle jumping - even in the rain - he LOVES this. Just gear them up properly.
Disco time - dirty dancing is the current favourite.
I have a huge sheet of mdf that I prop up on a box which he uses for racing his cars down.
Any sort of role play - at the moment it's mostly shops.