Diigo which is very versatile and allows you to add Diigolet to your Favourites Bar at the top of your browser...
... and so whenever you find a site you want to keep track of, you can do lots of things to the link other than just bookmark it. You can highlight, bookmark, add a sticky note, read later or share it, so there are quite a few good options. I particularly like the highlighting and sticky note options as often when reading I find parts that are especially interesting.
There's also Delicious which allows you to manage your bookmarks similarly but it doesn't have the extra features shown above. And the one that has really caught my attention lately because it is rather visual is Pearltrees.
Here's my Pearltree for you peek around and if you create an account feel free to pick any of my pearls - that's the idea, it's free, it's open and anyone can share and pick your pearls just as you can with anyone around. There's a premium option if you want to make them private and customise your page. I like mine being public!
Pearltrees is very easy to use too. If you install the Pearler - as shown below - in your brower bar all you have to do is click on it and then choose where you want your new bookmark to go.
This takes seconds! And what I find best of all is that you can create your pearls (folders) on the go. I'm a very visual learner and find that a Pearltree like this one caters best for my way of seeing things. I find it easier now to look through my bookmarks than before when going through my tags. We're all different of course so I'm not saying this is how it should be done, but my experience of it!
I've also recently moved to Firefox, so I'm now off to explore how you can save and sync your bookmarks with them. I just saw the intro video and I like the fact that you can sync them across computers. You can also do this with other bookmarking tools, but I like how easy it seems with Firefox. I'll report on this later on. In any case, I think I'll stick to Pearltrees because it also allows you to add comments to your 'pearls' and share them. I think it'd be perfect if there was a mix between Diigo and pearltrees and you could highlight and add sticky notes to your pearls! Here's hoping :-)