Fast/lightweight method of capturing leads/optins for an email list?

I currently use AWeber to host my email list, and then use OptinMonster for creating sign-up forms and displaying them on my site. This has all worked just fine with one small downside: OptinMonster is now the slowest thing about my website, which has now become extra fast after switching to GP and optimizing the crap out of everything.

OptinMonster is unfortunately the one thing that I can't optimize any further, so I'm wondering if there is a better option to use along with GP in terms of speed and performance? I'm not looking for anything fancy here. I don't need A/B testing or elaborate drag and drop editors or anything like that.

I just want a lightweight way to A) put a typical signup form in my sidebar and at the bottom of every post, and B) as an added bonus, I'd also love to a find a more lightweight method of doing what OptinMonster's "MonsterLinks" do, which is when you click on one of these links, it brings up a lightbox with a signup form while dimming the background of the page.

Any suggestions would be greatly appreciated.

Thanks.