Audiomove is really handy for sample & bit rate conversions
http://www.lcscanada.com/audiomove/AudioMove is a simple, easy to use GUI-based batch audio file copy-and-conversion program.
You just tell it what files to convert, what format to convert them to, and where to put the output files, and it does it. AudioMove has the following features:
1. Converts from any format that libsndfile can read, to WAV or AIFF format
2. Uses libsamplerate for high-quality sample rate conversion to various sample rates (11.025kHz-192kHz)
3. Supports 8-bit, 16-bit, 24-bit, 32-bit, or floating-point output sample widths
4. Specify files to convert using file requester or drag-and-drop
5. Multithreaded design for faster processing on multiprocessor machines
6. Pipelined dataflow for efficient resource utilization
7. Recursively batch-convert entire directory trees in a single step
8. Conversion-batch sizes may be arbitrarily large (e.g. thousands of files at a time)
9. Can be controlled from the command line (useful for invoking batch conversions from scripts)
10. No installation necessary -- just unzip and run (well, actually the Win32 version does come as a .msi file)
11. Qt-based GUI means AudioMove is portable to most major OS's
12. Open source (GPL); source code is available below
13. SUSE 9.1, MacOS/X and Windows binaries available below for your convenience.