< 18 lbs isn't going to be easy. i think the steeda's are like 22lbs. i found this a while back. these are all 18x9's but i think a lot of them are pretty ricey.
Buddy Club P1 Racing QF 14.8
RS Watanabe Cyclone 16.1
SSR Type-C (called Competitions in the US) 17
Dinan BMW (Fiske) 18
Wed's TC-005 18.6
BBS RCJ 18.7
BBS RG-R 18.9
Advan Racing RG 19
Enkei RC5 19.5
SSR GT1 19.7
Ro-Ja Formula 5 20
SSR Integral 20
BBS RS-GT 20.2
BBS RE 20.9
BBS GTII 21
Enkei RPO-3 21
Enkei RPM-2 21.1
BBS RG II 21.3
Enkei RPO-1 21.3
Enkei RPO-2 21.9
Work Meister S2R 22.3
BBS LM 22.4
BBS Super-RS 22.6
BBS Primadonna 22.9
MB Motoring WEAPON 23.5
Enkei ZXC 23.8
Blitz Technospeed Z2 24
Enkei Phalenx 24.2
Kosei Sniper 25
MB Motoring EXE II 25
Konig Tantrum 25.3
OZ Vela 25.3
MB Motoring VR1 26
Motegi Racing Touge 26
CCW makes some nice wheels. A lot of people use the CCW Classic for road racing. http://www.ccwheel.com/files/home.php
I think they can make about any size/offset you want.
If you are really concerned about weight, some tires will weigh more then others. I'm not too sure about street tires but as an example, my old 315 hoosier R3S03's weighed 10lbs a piece less then my full tread Kumho Victoracers.
Street tires are probably closer to each other though.
just to give you a $ range, my SSR GT10 18" cost me 4K when wrapped with kuhmo's on front and bfg DR's on back. ouch! so wheels alone were probly about 550-600 per.
and they weigh 25#, not 18!
you can get to 18# but probably not unless you go multi-piece forged wheels. that'll be pricey.
I know a guy with some custom boyd cottingtons that weigh 17#
I know I am going to have to spend a chunk. But in my view it's worth it. Even more so on a bigger car like ours.
I know a lot of muscle car guys don't bother with wheels weights most the time, that's a game for the ricers. But I travel through mountain switchbacks to get to work every day and I like to maximize the FUN.