If you (unlike the OP) need a specific number of records (which makes the CHECKSUM approach difficult) and desire a more random sample than TABLESAMPLE provides by itself, and also want better speed than CHECKSUM, you may make do with a merger of the TABLESAMPLE and NEWID() methods, like this:
DECLARE @sampleCount int = 50SET STATISTICS TIME ONSELECT TOP (@sampleCount) * FROM [yourtable] TABLESAMPLE(10 PERCENT)ORDER BY NEWID()SET STATISTICS TIME OFFIn my case this is the most straightforward compromise between randomness (it's not really, I know) and speed. Vary the TABLESAMPLE percentage (or rows) as appropriate - the higher the percentage, the more random the sample, but expect a linear drop off in speed. (Note that TABLESAMPLE will not accept a variable)
