Really, any. I know their are SSH apps, but what about other ones that will alert me of high VPS load, downtime (I guess there are ones specifically for that), or anything that'd allow me to even go as far as re-installing a server if needed. Maybe something that'd show me a list of servers I've added and show me info about them (mem/cpu/disk/bw usage).Managing which aspects?
Server monitoring without apps is free for at minimum 10 servers. I have at least 10 be monitored by NR right now.NewRelic looks promising, unfortunately the pricing does not for lowend usage.