We had a patio built in 2006 and had a company prepare the 'basement area'. Their last layer was a kind of sand, which when wet, hardens almost like concrete. He had some left and put it against our house where we had some chance of flooding and it has stayed there like it was concrete. I will try to get the name of it for you - I believe I saw it at Home Depot last year.

With pavers, you get weeds. Comes with them. Best you can do is fight to a draw.

Re-laying the pavers with a heavy layer of plastic between them and the sand reduces the amount of soil the weeds have access to.

There's roundup. Takes 2 weeks to work, and for dandylions will take 2 or 3 doses.

Road salt. May be hard on the stuff on either side. But it's cheap.

Fertilizer -- straight cheap nitrogen. Mix up a strong solution -- as much as will disolve in hot water. In effect you are burning the plants. Apply lightly, just enough to soak the root. Excess will do the neighboring plants good as it runs off.

Tiger torch. Lightly toast the leaves every 3 weeks.
Key here is to barely wilt the weeds. They use all their efforts to fix the existing leaves instead of starting new ones. Tiger torch and propane tank at princess auto, peavey mart, some BBQ stores.

Furnace oil. Gasoline. Environmentally unfriendly.

Really hot water, or steam.

Attacking weeds:
A wire wheel on a disk grinder works well for cleaning cracks. An ice scraper or a shovel if there is more weed than paver showing.

We use corn gluten (from a feed mill) which inhibits germination - I sweep it over the patio stones about twice a year - it is natural, not harmful, works fine, cheap _ 55 pounds for about $8
I have also heard that industrial strength vinegar (20%) works fine but have not been able to find it anywhere.
Hope this helps

I use regular vinegar 4%. Spray it on the cracks. It changes the PH level of the soil to a point where the plants (read ANY plant) can not process nutrients or water.
One or two applications while the weeds are small will inhibit growth.
It is said that the PH level will be changed for quite some time so it is not recommended to be used on the flower beds.
Dana