25. Western Digital
Fortune 500 Rank: No. 222
Revenue: $12.5 billion
Top Executive: President and CEO Stephen Milligan
Irvine, Calif.-based Western Digital moved up from No. 276 last year. In January the hard disk manufacturer beefed up its SMB storage business and channel efforts by acquiring Arkela Software, a developer of data protection software and appliances for small and midsize businesses.