Question: 55 gallon tank setup?

I'm slowly getting a 55 gallon tank set up for my two 5" axies. I already used Nick's instructions on putting down slate in the bottom, so I don't have to worry about substrate, but I'm trying to make a mental list of other things I need so I can get cycling!

One thing I definitely don't know about is what filter to use? Right now I have a Penguin Power filter (model 100). I taped a cut up water bottle to to decrease the flow because it is too strong for them, in the tiny 10 gallon tank I have right now. I really want to get them out of this setup as soon as possible. I'm guessing that it probably wont be a strong enough filter for a 55 long, however. Any suggestions?

Also, I was thinking about getting some live plants, but with slate at the bottom I'm not really sure what my possibilities are..

If you search the site for "plants," you'll find a lot of thread recommending easy-to-grow species that should do fine in the tank. A lot of us without substrate in our tanks affix plants to our decor (rocks/wood), and/or have floating plants.

Slate's a nice choice and should look quite lovely. As far as a filter, I use a Zoo Med 501 on one of my 55s and a Tetra Whisper 60 on the other. I have the waterfall diverted through artificial hanging vines like you would use for reptiles.

Moss balls work well anywhere. Java moss can be tied to just about any kind of ornament (driftwood, large pieces of slate, or stones just to name a few) or you can just leave it free floating as jclee suggests. Java fern can be potted or it too can be attached at the roots and should do well for you. If you choose to buy potted aquatic plants, be aware that sometimes there are fertilizers that could be harmful, so you may want to remove the usual packing and use some of your own.
See Plants for some suggestions. The list is at the bottom of the page.

Good luck and would love to see the set up once you have it all done!