i use home depot play sand... just make sure it's 100% silica sand, and wash it out really really good... in my 200g, 100g, 60g, 30g, 25g, and now my 20g palladium all have play sand... the plants love it, and it looks great... just make sure it doesn't get into the filter system some how...
there is some other stuff that aquarist look for, it's called colorquartz and it's made by 3M... it's heavier and comes in a bunch of different colors... but it's hard to come buy... some swimming pool building places carry that sand... and it ranges from $20-$30 per 50lb bag... but playsand is about $5 a 50lb bag... so it's all up to you...
good luck...