Holy haziness, Batman! Gotta smile at your question. As if there is 1 example of "great ad copy" that works universally for everybody and everything!

Effective writing is always precisely tuned to both the topic and the audience. Here we don't know what you're trying to say / sell, nor whom you're addressing. Who ARE those 20,000 people? What do they want? What do YOU want from THEM?

If you've got "targeted leads", great! At whom are they targeted? Retired people in Texas? Teenagers in the UK? Startup CEOs in India? Past customers of a defunct coupon website?

As a writer, the first thing I need to know is what I'm trying to say. Second, I need to know something about the people I'm talking to. Then and only then can I pick a style.

Giving an example of "great ad copy" in this case, given the utter absence of information, ain't possible, old pal.

But I'd love to help.

Writing short-form copy for brochures and landing pages is 1 of the services I offer. For me it goes hand in hand with name creation. Just another part of branding. Getting the copy right is quite important for you.

You can look at this as an experiment in getting signups. Even do some A/B testing, since 20,000 leads is enough to draw conclusions. But this isn't just a transaction. This is where you introduce yourself as a brand. So you'd better know who you are, what you're about, and how you want to be perceived. Don't blow this first impression!