I see some people throwing you both good and bad advice.
Living in South Beach, I'll give you alittle run-down on stuff in the area.
Lincoln Rd -- Street is closed to traffic-- lots of moderate++ priced restaurants that offer outdoor dining-- great place to "people watch". Check out Meat Market for a good steak, Carnivale for a cheap Filet+1/2 lobster special and out door dining, Doraku for decent sushi.
Ocean Dr.-- The preserved/restored scenic boardwalk where alot of art deco hotels and neon lights have been revamped (Think the scene in Scarface where he meets those columbians in the hotel). Much nicer now and very tourist. Check out Mangos if you like to dance or just watch their scantilly clad dancers. The Clevelander is a GREAT spot-- newly renovated and very popular. Outdoor bar w/ a pool, music, reasonable (for SOBE) drinks, good food, and awesome atmosphere.
Washington -- Alot of Clubs/Bars/Small restaurants are up and down Washington st in SOBE. Mansion and Cameo are the two "hot" clubs that seem to have stuck around. Expect a line, big tabs, and plenty of attitude from their half-ass staff. Less pretentious good times are Automatic Slims (a not-so-dive dive bar), Purdy Lounge (off the beaten path in SoBe on Purdy st) is an awesome bar to meet chicks and enjoy a very low key crowd.
Collins ave--
Alot of hotels, etc up and down this spot. Ranging from the massive Loew's Miami Beach to the small art deco hotels that line the blocks south of about 20th st. Check out the bars in the W hotel SoBe. The Gansevoort hotel has Club Louis-- but like all bars owned by the opium group (IE Mansion) expect big tabs and lots of attitude.
Dining--
Prime 112 -- Most popular high end steakhouse on the beach.... good reason for that one-- good luck getting a reservation.
Prime Italian -- sister restaurant to Prime 112, directly across from Prime 112-- nicer decor, easier reservations, almost the same menu. Figure $75-125 per person, but its worth it.
Smith & Wollensky -- Way way overrated steak house.
Nobu -- Excellent but overrated and way over priced.
Shoji Sushi -- Reasonably priced and high quality (approx $35-50 per person)
Devito's (owned by Danny Devito) -- decent but again Overpriced/Overrrated
Mr Chow
Phillipe Chow -- Restaurants are rivals-- the original chef from one went out on his own... both are considered EXCELLENT. Expensive though..
B & B -- Burger and Beer joint-- very trendy place for AWESOME burgers and huge selection of international microbrews. Prices are actually VERY reasonable. Parking is a problem-- Either Valet or just take a Cab here.
Joe Allen -- next to B&B is a local low key mid priced restaurant with excellent food and strong drinks. Not a "scene" just locals having dinner after work.
Big Pink -- 24 hr diner style food... great when drunk
Pizza Rustica / Ginos Pizza/ Etc -- all the 24 hour pizza places taste great when drunk.
DOWNTOWN---
Space -- if you wanna do X with a bunch of 18 year olds until 2pm the next day (yeah-- they're open until the next day...)
Nocturnal -- About the same as space... come get drunk here with 19 year old Jersey Shore rejects that got ID'd at the other clubs and couldn't get in.
Nothing but blow-out hairdo's and last-bodystyle M3's hangin out here LOL
Strip Clubs --
Gold Rush (downtown near space) 24 hours and full nude... Go in w/ a group and you can get away with SERIOUSLY bad behavior in this club. Wanna fuck one of the girls? It can be arranged directly w/ her... just remember that snatch is cheap in MIA. (Also.. the area is dicey at night time)
Tootsies -- Big and modern strip club in Miami Gardens (about 15-20 min north of downtown Miami). Less seedy than Gold Rush.
The Madonna -- in SoBe.... you would think this place would be GREAT.... Prepare for disapointment! Lousy strippers and heavy cover charge.
Hope this helps you!