In reply to Emergency-Pollution2. Thicker usually equates to better quality, but also becomes more expensive. Here are some specs I've accumulated on some of the more common brands and their standard cards in 4x6" format:

Name | Thickness**(Point)** | Card****Weight (#) | GSM
Amazon Basics | 7.8 | | 122
Exacompta | 8.75 | 76 | 205
Notsu | 16.875 | 130 | 350
Oxford | 7.2 | | 144
Staples | 8.3 | | 147
Stockroom Plus | 10.6 | 92 | 250
True Red | 8.75 | | 160
Wexford | 7.5 | | 135
Nordstrom Dumati 14 | 14 | 100 | 271
Nordstrom Dumati 17 | 17 | 120 | 325
Nordstrom Dumati 25 | 25 | 200 | 541