Stephanie,
The idea behind the services like this is to provide some site activity thus either stopping the site Application pool being unloaded because of no activity or starting up the app pool again if it recyled for some other reason.  Both of which 'hide' the longer start up phase t site visitors.
Any monitoring service that checks for the correct loading of a page will fit the bill as long as it checks the site at a shorter period than the time out on the app pool. Just point it at the 'keepalive.aspx' page in the DNN root and exclude this page from any statisitcal reports.
Some of these monitoring services will provide a basic service for free in return for you putting thier logo on your site.  Also check with your host they may provide some monitoring as part of your hosting package that might suffice.
HTH
Antony

pinging or http requesting of ur website to recompile the asp.net/dnn engine is the best approach

i tried  Snapsis PageBlaster, it is great in case one has a simple site, (i.e. no third party modules, with javascript), the content of that particular module disapears!.

i have upgraded my site from 4.3.4 to 4.3.6 and have noticed a considerable increase in recompilation of the site and obviously the speed,

so stick with pinging and  and upgrade .... u best bet!