Most recently, the system I used is as follows:
20 point buy, maximum ability value at this stage = 16.
Then, allocate 3 x 1d4 to abilities in any fashion (eg, 2d4 to Int and 1d4 to Con, or 3d4 to Str, or 1d4 to each of Str, Dex, Con).
Once all d4s are allocated, roll away, with total results over 18 being considered 18.
This provides what I consider a nice balance between random factors and player control. You can wastefully guarantee an 18 with a 16 + 2d4, or gamble with lower values allocated individual d4s.
On maximised, average results, this system closely approximates a 32 point buy.
For my upcoming Conan game, I'm probably going to go with the Conan heroic option of 8+1d10 for all ability scores.