For the free service, I'm looking for something that would notify me by email and SMS if the site is down or slow (within about an hour). So far it looks like http://aremysitesup.com/premium/ can do this. Pingdom is way too expensive for my needs right now.
I would love to support a fellow Hacker News reader. Does your app fit my needs?
Edit: I just re-read about having lots of little sites. I will consider a reduced-functionality (eg. as you say within the hour notification) but allowing more free sites as an option.
As you can see, you have a lot of sites competing with you (which means you have a market!). Now you need to distinguish yourself.
I'm having trouble finding a service that does the following:
* Offers me a free service that's suitable for sites that aren't that critical.
* Once I need a higher level of service, offers me a way to gradually turn up the service and payment.
Maybe I'm expecting too much out of a free service.
EDIT: I realize what my expectations are now. I think Google has spoiled me. Here's what I expect (and I think the web monitoring service that can offer this solution will likely win):
* Monitor an unlimited number of websites at a frequency of not more than 60 minutes. Will send an SMS and an email if the site is unavailable or too slow. (Maybe there is a cap on the number of SMS messages per month.)
* Offer very gradual price increases for increased service (gradual like this: http://site24x7.com/site24x7-pricing.html)