TextSplitter is an open source GUI utility written in C# for .NET platform. Designed to split the text file into multiple files for a specified number of rows or the size of the resulting file. Encoding of input and output files can be selected.
Works well enough. Quick and simple. (on a side note, the past-tense of 'split' is 'split', not 'splitted'. Sorry, it was irking me).
I use it.