This is something that I have been working on for a while now as I get bored at work. It stayed in a fairly simple state of only calculating the effects of healing gear and talents. Then I saw the amazing Paladin spreadsheet and determined that I could do that, too.
http://www.cat.pdx.edu/~murasaki/druid_spell_sheet.xls
I am currently working on implementing combat rules and will eventually give room for buffs and trinkets and such, but at the moment, you can simply add the buff information to your base stats.
Numbers so far have been fairly accurate. I am noticing some minor differences on spells such as Regrowth, which I believe to be due to rounding issues.
The "Time 'til OOM" information is something I've been tweaking for a while and I think I've found a sweet spot. You'll need to make sure that iterations are turned on, if it doesn't default when you open the spreadsheet. 100 and 0.001 seem to work nicely.
I am in the process of adding Balance spells to the sheet as well. Need to verify numbers and calculations, so I'm waiting for the servers to come up.