I see a lot of posts asking about damage comparisons, and I have done plenty of them for myself. Well, I got tired of fiddling with #'s and finally (no idea why it took me until now) decided to put together a decent formula. This allows you to plug in your damage bonuses, seeker, double strike, and the properties of the weapon. A separate variable for "bonus x on 19-20" allows you to add in modifiers gained by OC, ED (devastating crit, headmans' chop, etc), FB III, etc. It doesn't (yet) account for differences in off hand attacks (rate, bonus) or manuevers (cleave, manyshot, etc), but it gives a good apples to apples snapshot comparison where appropriate (like trying to choose between two weapons)
You will have to calculate some things yourself (i.e. holy is a proc worth 7, shocking blast is a crit proc worth 11 on a *3 weapon, etc). Put special % attacks (lightning strike) as a normal proc based on average damage. You can (if you want) add your glancing blows as proc damage also, but that will vary greatly with how often you get 1st/4th attacks in chain (disrupted by cleaves, moving, etc) so it can be added to get a rough idea, but will imbalance the stats compared to weapons that don't get them. So, all that said, you can plug this formula into a spread sheet with these columns:
bonus x on 19-20
total/swing = (((B1+B2)*(19+B3*(B4-1)+2*B5)+B16*(B3*B4+2*B5)+19*SUM(B6:B9)+sum(B10:B1 1)+B3*SUM(B12:B15))/20)*(1+B17/100)
Feel free to check my work and offer any criticisms. This can be easily enough modified to generate DPS #'s as well, but will take a little work.
*edited to update fields/formula to add vorpal procs)*