Fireline thread in the 6 pound test strength is probably the most versatile and commonly used size for beadwork.  

FL06CR125 - 6 LB Test Fireline Crystal .006 In/.15mm Dia, 125 Yards | 1 Spool
Sale
Berkley
$40.88 $16.99
FL06CR125 - 6 LB Test Fireline Crystal .006 In/.15mm Dia, 125 Yards | 1 Spool
FL06CR50 - 6 LB Test Fireline Crystal .006 In/.15mm Dia, 50 Yards | 1 Spool
Sale
Berkley
$15.75 $7.88
FL06CR50 - 6 LB Test Fireline Crystal .006 In/.15mm Dia, 50 Yards | 1 Spool
FL06SG125 - 6 LB Test Fireline Smoke Grey .006 In/.15mm Dia, 125 Yards | 1 Spool
Sale
Berkley
$38.96 $19.48
FL06SG125 - 6 LB Test Fireline Smoke Grey .006 In/.15mm Dia, 125 Yards | 1 Spool
FL06SG50 - 6 LB Test Fireline Smoke Grey .006 In/.15mm Dia, 50 Yards | 1 Spool
Sale
Berkley
$16.75 $8.37
FL06SG50 - 6 LB Test Fireline Smoke Grey .006 In/.15mm Dia, 50 Yards | 1 Spool