Have you discovered Picnik yet? If not, you must visit and create a free account. It might be one of the greatest sites on the internet! You can upload and edit your photos and create your own art for free! Of course many of the "better" options are only available to those with a paid membership, but look what I created today for free:
I searched the internets high and low for a suitable winter pool party invitation but couldn't find anything I liked that was suitable for my son ... this world is so girl-crazy! So I made my own. Certain information was obviously blocked out for privacy but you get the idea.
Using a free stock photo, I was able to download a pool water picture which I then uploaded to my Picnik account - and created the invitation from there. You can customize everything, including the finished size. I decided to use the 4x6 size for this invitation. It's saved as a jpeg file so I can easily upload it anywhere to have prints made.
I'm still debating whether or not upgrading to a premium membership is worth it, since I likely wouldn't use the site daily or even weekly. But regardless, it's pretty cool. Check it out when you can!