I love checking out farm and garden planning websites. There's a lot of great software out there, but I have yet to find something appropriately sized for a small farm (that doesn't cost a fortune!). I'm still working on developing my own excel sheet (which hopefully will work well enough to share in a couple of seasons), but in the meantime I came across the Smart Garden website. You can design plots up to 150'x150' or simply design container gardens. It even puts together your seed order and schedules a to-do list/calendar. Did I mention it's free?
Definitely worth checking out! See it in action HERE.