I've taken a look at several collage apps for iOS, and have been pleased with them. Having said that, Wrapframe (US$1.99) comes with some fresh ideas and more than a hundred templates to allow you to combine multiple photos into a single presentation. You can warp and wrap your photos to give them a fresh look, and apply any of 27 filters and/or text to finish off your masterpiece. Then you can save to your photo roll, or share them via Instagram, Facebook, Twitter and email.
Using the app is simple, and there is built-in help. Select a template, containing room for two or more photos in a style you like. Then select photos from your camera roll, or snap some with the iPhone or iPad camera. Once the photos are in place, you can apply filters or add text. One thing I don't like is that if you select a portrait orientation for a photo, the app scrunches up the image in landscape mode to make it fit, distorting the photo. As a result, you have to be careful about what kind of photo you put in to a particular template.
There are plenty of filters, but I'm getting to the point where most filters detract from a good image, and don't add to it. Text may or may not be needed to finish your collage. I think most photos won't require text, but it's nice to have if you need it.