H2O2 and Excel (as well as bleach and potassium permanganate) dips work well, assuming you get the right concentration and time to kill the algae without substantially affecting the plant. This is a little easier said than done, and different plants respond differently, so you'll get a wide span of recommendations.
If I want a quick dip, I use H2O2 or Excel. Otherwise, I greatly prefer AlgaeFix dips, which don't harm plants at all. Perform in a bucket at the recommended dose, and leave in a dark place for three days, then remove and rinse well. The dosage is 1ml per 10G, so for a 5G bucket, that's 0.5ml.
Which is hard to measure accurately, so I make myself a bottle of a weaker solution. 3 tablespoons of distilled water, 1 teaspoon AlgaeFix. This dilutes it by a factor of 10, so the dosage for that solution is now 10ml per 10G, or 5ml for a 5G bucket. 5ml is close enough to one teaspoon. Much easier.