Name of ISP: Lijbrandt Telecom
Country: The Netherlands
When does this problem occur: All the time (strangely enough ever since the big patch at the beginning of September). I do lag a lot more at peak hours than other times, but I get regularly lag spikes at any given time during the day

It also appears I'm not the only person using this ISP who's having this problem, as someone else with the same ISP already posted before me (post #425, page 43).