Jonathan Mayo has his Top 20 prospects in the NL Central, and yes, there are some Astros on it - namely Jonathan Singleton as Mayo's #1 1B prospect, and George Sprigner the #3 OF prospect.
And in this article, Mayo has his organizational preview (with a Top 20 list here, which you can click the link for Mayo's full write-up on each one):
#1 - Jonathan Singleton
#2 - Jarred Cosart
#3 - George Springer
#4 - Jonathan Villar
#5 - Mike Foltynewicz
#6 - Paul Clemens
#7 - Brett Oberholtzer
#8 - Delino DeShields
#9 - Domingo Santana
#10 - Telvin Nash
#11 - Jordan Scott
#12 - Tanner Bushue
#13 - Austin Wates
#14 - Jake Buchanan
#15 - Nick Tropeano
#16 - Juan Abreu
#17 - Kyle Weiland
#18 - Josh Zeid
#19 - Mike Kvasnicka
#20 - Ariel Ovando
We didn't come out here to play tiddlywinks, son.
-Hal Smith