Intel Core i3 3220
In late 2012 and 2013 the Intel Core i3 was a nice CPU for entry level systems. Dual-core systems were sufficient for most users that didn't play games or used high-end applications like video editting or 3D-modelling. Even most games didn't benefit from having more 2 cores at that time.
The 3220 runs at 3.3GHz and has hyper-threading capabilities.