The best programs in this group, i.e. the ones getting the best possible compression, are WinRK (using PWCM mode), PAQ8, PAQAR, Durilca and SLIM. At the moment WinRK (PWCM) and PAQ8 are the two best compressors of the five, but they are also much slower then Durilca and SLIM (to give you an idea; PAQAR in -8 mode does about 5-7 KB/s on a slightly overclocked AMD Barton 2800+). If you have files with embedded images (e.g. Word DOC files) use PAQ8, it will recognize them and separately compress them, boosting compression significantly. Also note all mentioned programs with the exception of WinRK are free of cost.