I use Dynamic3 to monitor our call center, allowing me access from anywhere at anytime for my agent's training needs! It is not overly expensive compared with other systems we have used in years past (such as C4).
The customer service has been good so far - easy implementation process but they made sure that their tech support team was available 24/7 if needed during this time frame which helped ease some concerns of ours after working through multiple vendor options over two months before choosing them!