To get the last Golden Egg you have to zoom out on Birdday Party level 18-6 and then you will be able to notice the Golden Egg standing on a ledge on the right hand side of the level. Use the first two Blue Birds and nail it with your Yellow Speedster.
Here is the Angry Birds Golden Egg #27 Video Walkthrough:
One step before we obtain all golden eggs, at level Mine and Dine 17-12 you need to Zoom out. Then you are going to notice a treasure high on the top of the second rock ledge. You need to burn your red and also white birds and after that use a yellow bird at a very high arch in order to clear the front ledge. Use the speed burst at the right moment in order to clear the first and second ledge and nick the top left corner of the treasure chest and get the Angry Birds Golden Egg #25
Here is a helpful Angry Birds Golden Egg#26 Walkthrough Video:
At Mine and Dine 16-9 zoom out and you can see the Golden Egg on the top of the cave which is on the right of the screen. First use your first yellow bird just to eradicate the stone above the slingshot. This makes for a bit easier shot, but there is no need to do that. You need to aim the second yellow bird and tap it the right moment to boost its its speed in order to nail the Golden Egg #24. Which is pretty tough so probably you will have to practive much in order to be successful!
At Mine and Dine 15-12 you have to zoom out! You can see the Golden Egg is on the ridge to the right of the screen. Once you notice it, shoot a yellow bird aimed high towards the ridge. The moment you want to boost its speed tap it in order to send it to the direction of the Egg.
At Ham ‘Em High 14-4 you need to zoom all the way out. Then you can notice the golden egg on a cliff at the right. After that send a yellow bird at a very high angle toward the cliff tapping it at the correct moment to send it up to the egg.
To get Angry Birds Golden Egg #19 you have to zoom out at Ham ‘Em High level 13-10. Then you will find the Golden Egg hanging above the level. Launch a white bird, and drop an egg at exactly the correct moment to fly up and hit the dangling egg. Needs to be pretty accurate.