I actually quite like R&B...well, not the chart rubbish like J-Lo, Christine A, Nelly etc but good stuff such as Rahsaan Patterson, Donald McCollum, Angela Johnson etc. as for punters asking for it, usually they're referring to the chart cack (especially if they're under 20) popular tracks (mostly) from the last 6 or 7 years include:
Black eyed peas-my humps, pump it, mas que nada
Pussycat dolls-don'tcha, buttons, beep
Usher-yeah
Nelly-hot in herre
Notorious big-nasty girl, Mo money mo problems
Beyonce-crazy in love
Destinys child-independent woman
Christina A-Dirrty
Justin Timberlake-Like I love you, rock your body
Sisqo-Thong song
Lemar-dance with u
Eve & Gwen Stefani-Let me blow ya mind
Next-Too close
Mary Mary-Shackles
50 cent-In da club
Blu cantrell & Sean paul-breathe
Snoop & Pharell-Beautiful
Mary j Blige-Family affair
R Kelly-Ignition (remix), Step in the name of love, Happy people
Kanye West-Gold digger
But you have to be careful, cos if it's a crowd who are really into R&B they'll probably want current/new R&B for at least 1/2 n hour, before moving into some of the "older!" classics, if it's mostly chav white kids then it's not too much of an issue
The line between R&B and Hip-hop is very blurred now also. Some of the tracks included above are really Hip-hop but as far as most requests from punters are concerned it's all R&B