Monitors your websites every 5 minutes, totally free. Get alerts by e-mail, SMS, Twitter or RSS. Add up to 50 websites. Monitors can be refreshed for an instant check with a click. Supports https and authentication with user/password. Relatively modern UI. The free account * supports up to 50 monitors * no SMS notifications * doesn't support escalations (e.g. when the first contact to respond doesn't acknowledge the downtime, a second contact is alerted).