One great feature of SDR software like SDR# is the ability to make I/Q recordings of the entire received bandwidth for later analysis. The problem is that these recordings can take up massive amounts of hard disk space. Jay Moore, the author of the RTL-SDR DX blog has recently been experimenting with methods for compressing I/Q files (2021 UPDATE: Jay's site has been abandoned, please use this archive.org link).
Jay tried compressing a test I/Q file with 7-Zip LZMA, Zip Deflate and FLAC. His results showed that FLAC compression was by far the fastest and also compressed the most in a test I/Q file with low amounts of redundant information.
Jay also discovered that it is possible to record "filtered" I/Q recordings using the RAW setting in SDR#. The RAW setting allows you to record an I/Q file from the tuned bandwidth selected within SDR# which allows for a much smaller file size.