I used to like half races, but the growing number of them just soured me. Based on my readings of mythology and genre fiction, those with mixed racial/species heritages resulted from powerful, usually divine, magical influences, not mere biology in action. So, from now on, there simply won't be any more Half-races in my campaigns.
That doesn't mean that there aren't ways to mix things up a bit.
I'm using concepts & mechanics combining elements of Bloodlines, PrCls and templates.
While no PC will truly be a "Half" anything, they may have a trace of some unusual, unearthly blood in the family ancestry. This will have effects on the character's innate abilities- for instance, you might not be able to be a spontaneous caster without some kind of lineage from beyond.
Mechanically, it will be like a 3.X PrCl or AU/AE racial class level- you take levels in the racial or, in this case, bloodline class and get the level related benefits. Unlike race levels from Savage Species, you need not take any levels beyond the first. Like a PrCl, there are no penalties for taking racial class or bloodline levels. The more levels in the class you take, the more power you get from your ancestry- evidence of the strength of the blood on your mysterious family history. Bloodline classes range from 2 to 6 levels.
half-elf breeds with a half-orc
Assuming that these are standard D&D half-human half-elves & half-orcs, a simple application of the Punnet square shows we'd expect to get 1 Human, 1 Half-orc, 1 Half-elf and one Erc/Olf? out of 4 offspring.