Bogwood and driftwood is always nice, you can look at some in you LFS, and as a bonus it is all natural and no two pieces are the same! And you could grow plants like Anubias or Java Fern on it. I would love to see a pic of the tank
Siamese algae eaters aren't really suitable for a tank that's not at least 4 feet long. A 20G Long is only about 3 feet long, so its a bit small for them, especially as they grow. Ideally, they should grow up to 6 inches long each. One of the real reasons for this requirement, is that they are a shoaling species, and should be kept in groups of 6 or so.