Wifi and lemon alien diesel.. both are awesome. I kept 1 wifi out of 10 that is killer. Smells exactly like lemon pine sol and has nice big flowers. Very in demand at the clubs.
LSD. Grows huge. longer flower period but very quick in veg. Yield will blow most plants out of the water if you get the massive stem pheno. Not seen often at the clubs. When done well is amazing. Alien hallucination is on the bay right now and I bet that woudl be a winner based on the lineage.
Blueberry. If you can find it.
AK47. <<- surprised nobody mentioned this one. Gets huge buds. A classic.
Pisces genetics candy queen. I really liked that one for size and aroma. that on eis on eht ebay right now but probably not for long.
I think the key is to have something people can't get enough of (kosher kush, GSC, WiFi, FPOG...etc), or something that people don't see ever that has an awesome bag appeal... LAD, Alien hallucination, Candy Queen... etc.