What is the quickest / easiest way to launch a new site (not currently bookmarked, and that you don’t necessarily want to bookmark) within DTP?
From a bookmark. 
If the URL is in the clipboard, press Command-N to create the bookmark, then click on it. If you don’t wish to keep it, delete it afterwards.
Thanks.
If it is one that is just in my head, that I know from memory, and that is not on the clipboard it seems then that creating a new bookmark would be fastest. Is there a keyboard shortcut for creating a new bookmark/link (I don’t see one listed in the menu)? Fingers crossed.
Actually, that’s backwards. It takes more time to create a URL bookmark that’s in your memory, but not in the clipboard. To do that, you could type the URL into the address field of a full-fledged browser like Safari, DEVONagent, Firefox, etc. Then click in the address field and press Command-C to copy the URL to the clipboard. Back in DEVONthink, press Command-N to create a new document with the contents of the clipboard, i.e., a bookmark.
There’s no keyboard shortcut to create a new bookmark document, and that would allow you to enter the URL.
Nor can you type into or edit the URL shown in the built-in browser’s address field. If you click inside that address field, the page will open in your default browser. That’s intentional. The built-in browser isn’t intended to be a full-fledged browser and doesn’t have all the features of Safari or Firefox or Camino or DEVONagent.
So here’s the kicker. To open a page in the built-in browser, select an existing document within the database – a bookmark, an HTML document or a WebArchive document. If there’s a link in the page that opens in the internal browser and you click on it, the linked page will now open in the internal browser.
I like the contextual menu options in the built-in browser for capturing data from the Web. I can quickly and easily capture selected rich text/images or HTML or a WebArchive of the page.
So I’ve got more than 200 bookmarks of sites that I frequently visit, in my database. Note that, once a bookmark has been captured, it’s name can be edited without affecting the URL. So my bookmark for Science Magazine is named Science Magazine, rather than the URL for Science Magazine.
How did I capture those URLs as bookmarks? From another browser (or from Edit > Capture URL within DEVONthink, followed by Command-N). I can either select the URL in the address field of that browser and press Command-C to copy it to the clipboard, then jump to DEVONthink and press Command-N to save it to the database. OR select the URL in the browser address field and drag it to the desired location in the floating Groups panel (Tools > Show Groups). OR select a URL in a rich text document, copy it to the clipboard, then in DEVONthink choose Command-C to create the bookmark document. Takes maybe 2 or 3 seconds, which is a fraction of the time I spend deliberating as to whether I want to bookmark the site.
What’s the advantage of having bookmarks in my database, as opposed to bookmarking them in my default browser? First, I don’t like to keep hundreds of bookmarks in my default browser, as that gets clumsy. Second, it’s much easier to organize my collection of bookmarks in my database. Finally, I can make searchable notes and comments about a site in the Comment field. You should see some of my comments about Web sites that use a lot of junk science, for example. 
So first and most importantly, thank you for yet another thorough post in response to my question. You’re making this program much more useful to me than it would otherwise be.
What I meant was that IF I have a url in my head (and not on the clipboard), which is commonly the case, especially on the early end of my building my database, it seemed to me that being able to create a bookmark from a fresh url by typing would be the quickest. A drag and drop from the browser would be a nice maybe someday.
I’ve gathered from a couple of your posts that you do science research. What sort of research/science do you do?