What kind of thing is it? Different monologues lend themselves to different things.
"Earshot"
Buffy: I don't think about you much at all. Nobody here really does. Bugs you, doesn't it. You have all this pain, and all these feelings and nobody's really paying attention...Believe it or not, Jonathan, I understand about the pain...My life happens to, on occasion, suck beyond the telling of it. Sometimes more than I can handle. And it's not just mine. Every single person down there is ignoring your pain because they're too busy with their own...The beautiful ones. The popular ones. The guys that pick on you. Everyone...If you could hear what they were feeling. The loneliness. The confusion. It looks quiet down there. It's not. It's deafening.
"The Body"
Anya: (desperate) But I don't understand! (crying) I don't understand how this all happens. How we go through this. I mean, I knew her, and then she's, (sniffling) there's just a body, and I don't understand why she just can't get back in it and not be dead anymore. It's stupid. It's mortal and stupid. (still teary) And, and Xander's crying and not talking, and, and I was having fruit punch, and I thought, well, Joyce will never have any more fruit punch ever, and she'll never have eggs, or yawn or brush her hair, not ever, and no one will explain to me why.
"Potential"
XANDER: Aw, I'm just thinking about the girls. It's a harsh gig, being a potential. Just being picked out of a crowd, danger, destiny, (grins) plus if you act now, death...Yeah. They're special, no doubt. The amazing thing is, not one of them will ever know, not even Buffy...How much harder it is for the rest of us...Seven years, Dawn. Working with the slayer. Seeing my friends get more and more powerful. A witch. A demon. Hell, I could fit Oz in my shaving kit, but come a full moon, he had a wolfy mojo not to be messed with. Powerful. All of them. And I'm the guy who fixes the windows...I saw what you did last night...You thought you were all special. Miss Sunnydale 2003. And the minute you found out you weren't, you handed the crown to Amanda without a moment's pause. You gave her your power...They'll never know how tough it is, Dawnie, to be the one who isn't chosen. To live so near to the spotlight and never step in it. But I know. I see more than anybody realizes because nobody's watching me. I saw you last night. I see you working here today. You're not special. You're extraordinary.
"End of Days"
ANYA: Well...there was this other apocalypse... this one time, and... well, I took off. But this time, I don't...I don't know...Well...I guess I was...kinda new to bein' around humans before. But now I've... seen a lot more, gotten to know people... seen what they're capable of, and... (shrugs) I guess I just realized...how amazingly screwed-up they all are. I mean really, really screwed-up in a monumental fashion...And they have no purpose that unites them, so they just drift around, blundering through life until they die...which they...they know is coming, yet every single one of them is surprised when it happens to them. They're incapable of thinking about what they want beyond the moment. They kill each other, which is clearly insane. And yet, here's the thing. When it's something that really matters, they fight. I mean, they're lame morons for fighting, but they do. They never... never quit. So I guess I will keep fighting, too.