Timeline: 6-8 Months

Plan hotel accommodations for out-of-town guests*
This is actually a pretty easy task, although it may seem annoying. For this Hotel Planner is your best bet. You just input the information for your dates and what you need, and local hotels will "bid" you a price for each room. When reserving a block of rooms, the most important thing is to make sure that you are not financially responsible for the unused rooms in the block. Most hotels will give you a discount and a link or contact person that all of your guest can go through to reserve a room. Typically they will reserve a set amount of rooms for your date, so your guests are guaranteed a room if they book there. Also some hotels will give you a free wedding night suite with the block, so negotiate.

Finalize guest list & send Save-the-date cards*
The guest list should obviously be completed before you send your save the dates, unless you are splitting the list into an A and B group and don't really care if your B group receives a save the date. Also, make sure you have your hotel block and website up, so that you can put the information with your save the dates. Usually save the dates are sent 6-8 months before the wedding.

Book photographer and videographer*
Really amazing photographers get booked way ahead of time, so if you have your eye on someone and if photography is really important to you (which it should be) get this done asap. Sometimes the photographer will also do the videography and a lot of brides are not even having videographers now, so the photographer is really the main goal with this task.

Create your wedding registry
Same as the wedding website and hotel, you'll want to have this done generally around Save the dates, just so the info is on the website, which will be on your save the date. This can probably wait for 2-3 months before the wedding, because most people won't start shopping until last minute.

Order wedding cake
You really just need to book your cake baker and do your taste tests so you know you have someone that can give you a cake for the date you need. You should have a general design in mind, but it's really not necessary to have the whole cake planned to the tee.

Book ceremony officiant
This is pretty important if you don't have a lot of officiants in your area and your date is during season.

Select bridesmaids’ dresses
Bridesmaid dresses take around 2-4 months to come in depending on where you get them, so its helpful to the bridesmaids and your sanity to get this done early. At the very least decide your color and general style and the price range that is doable for your bridesmaids.

Book florist
Again, not too important but you don't want to put it off to the point where there's no one left to do your flowers. Decide whether you want to do DIY or are going to go with a florist, and have a general budget and idea of what you want.

Book DJ and ceremony musicians
In most towns there are tons of DJs, so if it's not too important to you, this can be delayed a little bit. You should know a few price quotes and have it narrowed down to a few DJs though. Ceremony musicians are pretty scarce for the regulars, so if you really want musicans this should be done by 6 months.

Book wedding day transportation
Not a necessity, but if you are using limos, vintage cars, carriages etc. make sure you know what you want and you'll probably want to put a deposit down around 6 months, just to reserve your date.

A word of caution: Just because some of these timeline items aren't too important and I say you can push them off, doesn't mean you should. I did for my wedding and it worked out well, but that's because I was a good planner and knew which vendors I wanted ahead of time, I just didn't officially book them. If you do leave these tasks to be done later, just be aware that you will most likely be a little stressed out about having so many things to do. You would be surprised the amount of little things you don't think of having to do until the month of the wedding.