(This one is about a month old, written while I had ESXi installed on my system.) As a hobbyist (and student), I don't have a lot of money to throw at hardware purchases so that I can work with VMware's ESXi. As such, you work with what you can. In my case, SATA hard drives. I received one from a friend, to include as an addition to an already running system.
Problem was, before releasing it, he'd used a secure wipe utility on it. When I attempted to add the drive as a second datastore, ESXi balked because there was nothing on the drive, not even the partition table.
Fixing this involves running a drive partitioning tool of some sort. Luckily, I had a copy of the Ubuntu Live CD ISO in my datastore. By creating a temporary VM and booting from the CD, I was able to partition and format the drive, all without having to reboot the host machine.
In short, if you can afford the space, it's a good idea to keep your various source ISOs and tools ISOs in a folder in your datastore. It's probably not a bad idea to have the burned CDs handy too.