crj705
Be aware that you are limited to 90 days stay every 6 month period unless you have a non-immigrant visa
This rule was changed in 2008. Now no longer the case. The tourist visa validity is currently either 15 or 30 days dependent upon whether you enter via land or air (and further complicated by which passport you carry).
There is no restriction on the number of 'back to back' tourist visas (at present!).