I know Felix and Cipriani's downtown have happenin' Sunday night scenes, but where else can I go for some good wine and a good crowd that's happenin' in Manhattan?

I'd try Pastis on 9th Ave at little w. 12th st.
see [www.newyorkmetro.com]
or www.pastisny.com

Of course there's always the Gaslight but you probably been there done that. I here Snitch is always a great place to see some good rock n roll even on Sundays.

are you looking for a restaurant, a bar, a club?

My sister just told me that Freeman's is a good place to go on Sundays (it's apparently so trendy right now you have a hard time getting in to the place any other day).
Freeman’s
8 Rivington St
New York, NY 10002-1235
(212) 420-0012
here's a review of the place:
The Scene
Down a dark, shadowy alley just off Bowery, the handsome, scruffy-faced men and understatedly glamorous women of the Lower East Side gather to drink wine, crowding around antique wood tables. Worn plank floors and painted cement walls, fit with moose, elk and other assorted taxidermy, give the place a quirky edge, as do the tattoed, waifish servers, who are also professional and expedient.

The Food
The affordable menu's inspiration stems from retro party appetizers and Midwest hunting lodges. Take the three best starters: nicely gamey wild boar pâté served with a few smashed raspberries and cornichon; baked artichoke dip thick with chokes; and Devils on Horseback--savory blue cheese-stuffed prunes wrapped with bacon. Whole roast trout, stuffed with thyme sprigs and served with lemon, is simple and perfectly executed; macaroni and cheese has lots of addictive crunchy Parmesan bits. Finish with the warm chocolate brownie a la mode.