The issue with supplementing probiotics is stomach acid. Some strains make it through alright, and others are developed to survive, but unfortunately many can't withstand the acid of our stomach.
Jarrow makes a great 10 strain, 50 billion CFU formula with an acid resistant capsule and a 'jell forming matrix' to overcome this. I've had a lot of success using it, and it's really not all that expensive on amazon.
It's called Ultra Jarro-Dophilus
Just as important is the Bacillus Laterosporus (B.O.D) strain. You can get this at The Global Healing Center, and it's called Latero-Flora
This same site also offers a 23 strain, 50 Billion CFU formula called Floratrex.
Last but not least, the Saccharomyces Boulardii yeast is something you wont want to be without. Jarrow has one that includes MOS (MannaOligoSaccharides) A prebiotic.
I've had a surprising amount of success with the above 4 over the last 6 months.