Well no 2 programs will ever be 100% accurate at proving stability - but Prime95 and LinX combined are a damn good start.
To start, a LinX run with at least 50% of your RAM for an hour should get you a baseline of stability. After you pass that, run Prime95 small FFTs for 4-8 hours (your preference, but I usually run 8 hours). If you can pass both of those tests you're on your way to having a stable system. I've yet to put a system together that could pass those two tests combined and move on to fail something else.
Gigabyte Z68XP-UD4 | 2700K @ 4.4 GHz | 16 GB G.Skill Sniper DDR3 1600 | 7970 | PCP&C Silencer 950 | 750 GB HDD w/ Intel SRT | Cosmos II