We a looking at downsizing our garden this year but I want to keep the plot as weed free as possible.

I need some suggestions for a ground cover that is not to labor intensive. Years ago someone told me about a clover to plant but I can't remember the name of it.

White clover would work as a sort of permanent cover crop.

So does permanent mean it grows back yearly or it is hard to kill?

Perennial, yes (not all clover is perennial, FYI).

No, plow as usual. You may develop a slight seed bank, but you will get that no matter what if you don't keep up with things.

If you want to work it a bit more (as in a couple times a year) you could do a field pea/buckwheat mix. It would dramatically raise the N as the field pea would fix N (nitrogen) from the atmosphere while the buckwheat takes the N from the soil and locks it up in the buckwheat (the N from the buckwheat then goes back into the soil after you till it in), but it tricks the peas into fixing much more N from the atmosphere. If you do keep knocking it down and re-seeding before the buckwheat goes to seed, you will dramatically increase the organic matter in the soil, keep weeds at bay (both field pea and buckwheat drown out weeds), and build a lot of N, without creating a seed bank from letting something like clover go essentially wild.

I should say that many cover crop combos are available. If you are just looking to keep the weeds down, the biggest thing is to keep something covering the ground very well (like clover), but still working the soil 1-2 times or so per year (frequency depends on cover used and your growing season length) to not let your cover get away form you, and keep the weed seeds germinating so you can kill them off.

I should have asked as well in the beginning: How long are you letting the soil rest, how big of a plot? If you want a "set and forget" style solution, you could buy straw and heavily mulch the area. 

If you do that, would be a GREAT idea to put a few inches of manure of choice down first, then cover with straw mulch @ about 5-7 inches or so deep. Would have an awesome garden bed in a year or two 

Thanks for the reply's, I think I will try the pea/buckwheat mix.