A successful wedding is as close as you smartphone.
Here are some helpful phone apps and web sites:
WeddingHappy (free, but also has $3 in-app upgrades) does it all. No, seriously...it does everything as long as you have an iPhone.
Wedding Budget (free at iTunes) helps you keep track of costs and if you turn your phone horizontally...Bam!...you get a pie chart.
Evernote.com (free; premium is $5 a month) is great for keeping track of everything as a sort of digital home, not to mention updating your friends and family. Also check out Awesome Note ($4 on iTunes; lite version is free) and Groups (free on iTunes).