A couple domain registrars I have used that may offer what you're looking for are Directnic.com and Godaddy.com
If you have a web page that is hosted by your ISP you could use free domain masking offered by Godaddy and it will look as if people are going to your domain but they are really at your ISP hosted page.
Directnic has two free options. One option will forward people to the site hosted by your ISP. A URL change will be visible to your ISP hosted site.
The second option will put visitors in a invisible frame and your domain name will remain in the address bar even though people will be viewing a page hosted by your ISP.
Many registrars offer forwarding and masking services. Don't be afraid to hunt around until you find the right fit.
PS Remember you can't change registrars for 60 days after buying a domain or transferring from a different registrar.