You'll find the tools here amazing, read lots of blogs to motivate you and promise you'll stick with it for a minimum of 30 days... once those days are past and you see the results, you'll have no problem at all finding the motivation to keep going!!
I have been on sparkpeople and following their calorie guidelines for 24 days now and have already seen a drop of 11.8 pounds! (seriously, 11.8... i count every ounce I can... lol)
I am not getting married myself but am a wedding photographer so I know what you're going through. Just remember that on your wedding day you'll feel fabulous when you've hit or come close to your goal and that feels much better than chocolate (chips, mcdonalds, pepsi, etc) tastes right now! :)
Good luck with everything and if you need any advice, just feel free to ask. Trust me, I've seen it all! lol
Hugs to you!