Cost Effective Bulk Email Sending Solutions

I am working with reliable, cost effective email marketing solutions, running sending apllication through a data server and sending through multiple smtp servers with IPs on rotation. Does anyone have any recommendations on their favourite sending software (Interspire, Sendy, Mailwhizz, etc)? And would anyone care to share their experiences with bulk email sending?

I started using Ongage - it's a single platform where you can add multiple ISP/STMPs under one "roof" and has many customization/Segmentation options that I didn't see in other platforms