So it sounds like we've established you may be able to orgasm from G-spot stimulation, but that's not your only option.
Clitoris or no, some sound advice is to get to know your body and what works for you, and at the end of the day the clit is just one of many erogenous zones. Some of the others don't provide such "easy" orgasms - but you work on them and you'll get there.
As Nat&Tom point out, some hefty vibrations applied to the vulva may work - no doubt for those with a clit, this comes into play here, but there are so many nerve endings in the whole area that this may well work for you. The doxy wand is a firm favourite for strong vibes, but LH also have the rockbox on a crazy price at the moment, and that is so incredibly powerful.
My OH really gets a lot of pleasure from penetration of bumpy and ridged dildos - and only just inside the entrance to her vagina too, something like the
G-spot has been mentioned above, so won't say much more, but the L'amoursose Rosa is teh best we've tried in that respect.
Have a google and read of your AFE zone (or A-spot) too, that provides for some good orgasmic fun too, C-shaped and heavy works best for us, like the pure wand.
Anal is a possibility too - there are reports of women orgasming from anal penetraton, but even if thats not successful (it doesn't for us), having something in your bum makes your vagina tighter and thereby more sensative to stimulation.
It is known for some people to be able to orgasm from nipple play, so experiment there too - maybe start with some suckers, go on to clamps and whatever else takes your fancy. Thats the key really - relax and experiment (ohh and lube where appropriate)
links
doxy - http://www.lovehoney.co.uk/brands/doxy/
rockbox - http://www.lovehoney.co.uk/product.cfm?p=31069
dildo - http://www.lovehoney.co.uk/product.cfm?p=29001
Rosa - http://www.lovehoney.co.uk/product.cfm?p=30909