I'm practically a poster child for ADHD, so I've had to learn a lot of tricks to remind me to do things. Here are some of the ones I use for doing online tasks.

The easiest way is to create a Word document or web page with the links to the sites you want. I remind myself to go to it by having a recurring Outlook task that pops up a message containing a link to my Word document or web page. Next to each link to the sites, I include username and password (obscured, just a hint so I know which password I used). Every morning Outlook pops up with a link to the web page and I can go through the links.

The nice thing about creating your own page is that you can group tasks. For example, I have a grouping which is "software that I have paid for". Each time I pay for the software, I add a link in this section with the site address, plus any other relevant information about the license or site. If I need the software installed on a new computer, I have all the installation information at my fingertip. I also have a grouping for "Daily Tasks". I put the groupings in an HTML table at the top of the web page, but it could as easily be a series of hyperlinks at the top of a Word document. Then I use Dropbox to make my links page available to me anywhere I go. All I have to do is remember my Dropbox password  :D

Another technique that I use if I want to make sure I don't accidentally miss any critical sites is to set up Outlook reminders to come up every morning, one per critical link. If I don't have time to go to the site when it comes up, I can click to have it remind me in half an hour or so.