Firefox (Windows Only) - Firefox's default new tab page presents you with a 3 by 3 grid of recent sites, but you can't really tweak it much. New Tab Pro offers up a more customisable alternative.
New Tab Pro's new tab page looks similar at first, but it includes (unfortunately ugly) buttons on the sides that can add or remove rows and columns of recent site thumbnails, so you can see the number you want. You can also limit the recent bookmarks to view only sites visited that day or that week, which is a nice touch that isn't available on the default new tab page. It's a simple little extension, but it's worth picking up if you aren't happy with Firefox's default solution.