Gophone, an AT&T prepaid service, offers unlim talk/text and 2.5gb of high speed for $60.
Cricket, an AT&T MNVO, offers unlim talk/text and 3gb of high high speed for $50 ($45 with prepay option which charges your credit card a little earlier and saves $5).
Note that Cricket is an MNVO, so their service is routed through a proxy which contributes to higher average ping times. Plus their download speeds are throttled to 8gb for LTE and 4gb for HSPA. I'm on Cricket's 10gb plan which will run me $55/month.