GBL, but that is probably just as hard and just as illegal to get as what GHB would be.... Unless your are located in Asia or a couple of European Countries.
I to am interested in finding another similar compound to GBL/GHB as I am located in Australia and it is extremely difficult to come across over here as of late.
I prefer GBL to GHB as I like the spinning effect and the amount of shit I talk on it and I only have to have 2mL to feel pretty damn fucked instead of like 4mL - 5mL of an awful tasting liquid....