My sister recently became engaed any ideas for a cake?Thanks in advance 
One of my favorite cakes for engagements is the ring box one. It's a square cake fashioned to look like the bottom of a ring box with the ring in the center and a rock candy diamond. I've always wanted to make one. You can also try a gallery search. Lots of ideas there...
http://www.cakecentral.com/cake-decorating-photos_search.html
you can get some inspiration from how he proposed and go from there.
I recently did one for my cousins engagement party. It was a copy of one that someone else on this sight had done......2 heartshaped cakes separated by wine classes instead of pillars. Everyone loved it and it was pretty easy to do. Take a look in my pix.
Okay, this one is a little different, if you like to think outside the box a bit. How about a cake that looks like a nautical book, titled "How to Tie the Knot" with a picture of a knot on the front. You could list the happy couple as the co-authors. 
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