Shhh! Don't tell JewishGuy, he thinks this is so gross and annoying (I think). I like to buy herbs at the grocery store and set some aside to root and eventually plant. Cilantro was something I tried once but it just rotted in the jar. Well, I'm trying it again, this time because when I bought it it had its roots still intact.
It's gross because last year I rooted and planted beans, garlic, and onions, only to completely forget about them when they were moved to another room, and they ended up dying and rotting.
I've also put some spearmint in a jar to root. Apparently spearmint is one of those weeds you don't have to really take care of and will root at the slightest opportunity. I got the spearmint at the farmer's market and it might be a little dry, so I don't know if it will want to come back to life.
I almost bought some basil from the farmer's market to try to root but I know that doesn't work so well. I will have to buy a basil plant, especially since our back patio gets good afternoon sun.