I also use something like Psions, mainly rolling, but rounding up or allowing a reroll or something if they are below average. I have run campaigns where players get the (round down) average hp each level. For some reason I like this method for gritty, low magic campaigns; I guess because the lack of magic leaves less to offset the result of high or low hp rolls.
I once read in an old Dragon issue of an interesting hp system. Every level, you reroll all your hit points. If you end up with less than you had before, then you get 1 + con mod hit points added. This pushed PC hit points to a bit above average over the long haul, and has the advantage of giving even realy low hp charaters hope in the long run. Of course the down side is once in a while someone would get a realy good roll and have their hp balloon up to giant proportions.
I once read in an old Dragon issue of an interesting hp system. Every level, you reroll all your hit points. If you end up with less than you had before, then you get 1 + con mod hit points added. This pushed PC hit points to a bit above average over the long haul, and has the advantage of giving even realy low hp charaters hope in the long run. Of course the down side is once in a while someone would get a realy good roll and have their hp balloon up to giant proportions.