File Splice is an easy to use app that will merge/impose PDF files (more file types on the map) in custom formats. You have the ability to create a layout in a few simple steps and input the page size, margins, bleed, spacing, and crop marks. Upload files in the the browser via the webftp or connect via traditional ftp for large quantities. Functionality includes the ability to:

Create custom layouts. Set build (page amount) sizes. Adjust quantities and overages on the fly. Insert custom cover sheets before each file. Auto generate cover sheets with file names for quick sorting/collating. Turn off or on crop marks. Apply lossless compression. Form a team and work from multiple locations.

There is no contracts, software to download and support and setup is free.