Aside from sempervivums, one of the other succulents that can be grown in zone 6 would be sedums which are ground cover succulents which I use to highlight the edge of my garden stream. These proliferate very fast, and tolerate almost any kind of conditions so therefore I plant them straight in clay soil, knowing that they will grow well.
Here's my original species. I don't know the name of it, but if anyone can help me out with it, any help would be greatly appreciated. This covers an area of about 1ft by 6ft. Just found out it is sedum 'Sarmentosum' thanks to Cheryl
Since I've been doing some spring trades this year, I acquired 4 more species which have started growing pretty nicely after getting them planted. I'm giving them all at least 6ft by 1ft of space to spread, and I know sedums can spread quickly once established.
Sedum sexangulare: you can tell by the bushy ends where the new growth has occurred so far.
Sedum rupestre Angelina: This one have some nice vibrant colors and it has also come along nicely.
Sedum reflexum blue spruce: This one has the largest stems.
Sedum spurium 'Tricolor': Now this one looks like the odd one out compared to the others, but they will look nice once they all spread out a bit.
Now to help them proliferate, I plan on taking clay soil, and laying it over them so that they can take root, and make more plants. Another thing that I use on most of my plants including the sedums is aerated worm tea which I brew in a 55 gallon drum. I use a mixture of worm castings, humis, top soil, garden soil, and brew it at 80F with a large fish pump, using molasses and seaweed to promote more fungi. You can tell by this picture how dark the brew is, and this stuff makes plants look like they are on steroids.