OxyNinja has the obvious design library, but the real power of it is the utility classes. Check out the YouTube channel Digital Ambition. He has done a bunch of tutorials lately that were all made possible by OxyNinjas framework.
Hydrogen can really make things a lot faster by enabling a ton of keyboard shortcuts. It take a bit to get used to them, but it can save you a couple of seconds to do tasks you do all the time. If you want to add a div, SHIFT+D will do it without you having to take your hands off the keyboard. If you want to duplicate an item elsewhere on the page, you can just copy and paste, rather than duplicate, and then drag the duplicate elsewhere. These sort of efficiency improvements can help, not just in saving you time, but keep your momentum going when you're in a groove.
OxyElements is just great to add some additional modules. Some of them are really handy. I have to be honest; I got that one for a lot less money that the current price. It's worth the money, but the higher initial price makes that harder to justify if you're building a few sites here and there. I think it was like $69 when I got it.