Mange and scale your infrastructure with Scalr.

Unfortunate typo in title but I can vouch for scalr.

Used it since the early paid beta. Compared to the likes of rightscale it's a bargain. Alongside all the expected things like ami creation and cluster (aka farm) configuration the scripting features and automatic DNS management make life much easier. Their quality control used to be a bit hit and miss and it sometime felt like we were testing their functionality for them. I also had the impression their European DNS performance was poor (never validated). For the money though they were still a cost effective way of managing large ec2 clusters.

The open source version used to be a real pain to setup. Given the relative cost of setting up and running your own install I'd go with the paid version.