Best tool for the job I've found: Open Source CSV File Splitter (OSV)
Very quick and easy to use. Specify lines per chunk file and you're good to go.
Keep in mind many office suites (OpenOffice/LibreOffice) have row limits around 65k (pre 3.3.3: limit is 65,536 rows | 3.3.3 and later: 1,048,576 rows)
In Excel 2010, the maximum worksheet size is 1,048,576 rows.