View issues that are assigned to me?

It sounds like you're looking for https://github.com/issues/assigned.

The easiest way to get there is to click on the Issues link at the top right of the GitHub UI, and then the Assigned tab at the left side of the screen:

You can also use the assignee key in the search bar manually, e.g. assignee:panthro.

6 years later (January 2020), you also have the @me search syntax.

See "Search by @me"

That means Chris' screenshot of the "Issues" search field would now read:

state:open is:issue assignee:@me 

No need for "assignee:myuser"