PDFCombo for Mac OS X 10.6+ can combine PDFs while preserving table of contents
PDFCombo version 1.0.3 adds three new features:
You can edit the Table of Contents (TOC) entry for the PDF directly in the table's first column. This is especially useful when using the Print dialog in other applications to Print as PDF to PDFCombo, where the PDF filename may be too generic.
New option to preserve or discard existing TOC in PDFs, where if you choose to discard existing TOCs, the generated combined PDF will only have top-level TOC entries corresponding to first page of each input PDF.
Keyboard shortcuts CMD + S for saving combined PDF to disk, and Option + CMD + S to save to temporary PDF.