Why does my entire system wait for my external drive to spin up?

I have an external drive which likes to spin down when it hasn't been accessed in 15 minutes or so. All it contains is media like movies, whereas 95% of my regularly used files are on my internal hard drive.

Why, then, does Finder stall for a good 5 seconds when accessed while it waits for this external drive to become ready to be accessed? Surely it should look at the local files first before adding in results from my external HDD when required?? Is there a way to change the order in which it gathers these results?

I've already tried omitting the external drive from Spotlight searches in the preferences, but it still happens.... Is there a fix for this?

Thanks, I'll give that app a try but I already have a similar app (UnDock Now) that lives in my status bar. Also, this app doesn't really solve my problem, which is that the ENTIRE system halts while this one drive (even when not being accessed) spins up.

I know I said the drive is hardly ever used, but that's not strictly true. I do need to access it about twice a day, and so un-mounting and re-mounting constantly will probably amount to the same time taken up by this current problem....

Any other ideas?