New guy, since we've been through all that in a previous thread I'll give it my go.
I'd say to plan for a reef tank. You say you want a little more then fish and rocks. That sounds great. Keep in mind that it will be cheaper to set up the tank for what you want in the end instead of starting with one tank and converting it to another. You have a few options. I'd recommend checking out http://www.nanotuners.com/
it'll make your head swim. There are some really great set ups turn key available there.
My 20g home build.
600gph overflow box.
20g sump/fuge in the stand
ASM miniG skimmer http://www.thatpetplace.com/MainPro/...49BB+0578+0023
These can be had a little cheaper and can be added a few months down the road.
Lighting. 150-250w metal halide 12-15K with PC or T5 supplemental lighting in 20K http://cgi.ebay.com/30-inch-250-HQI-...QQcmdZViewItem
My friend bought 4 lights from this guy and has loved the quality and results. Much cheaper than anything you can get in the LFS. Thei light will meet ALL of your demands as your tank grows into it. Can also be moved up to a 50g if you ever upsize. I realize this is very expensive but lighting is the single most important part of reef keeping besides clean water. Again you can begin cycling the water without a light and get this a few weeks before you are ready to establish the tank. I think he offered a 150w with some PC bulbs for about $300 if you call him. My friend Kyle ordered the 15K bulbs he sells and loves them.
Return pump from sump, Eheim 1048 (marine depot or Big al's have great prices) This is only to lift the water back to the tank. Not to add flow.
Seio M620 for internal flow.
20 lbs Carib sea dry aragonite or oolite.
5 lbs of good live aragonite from LFS (generally $2 a lb) to seed the tank.
15-25lbs of quality live rock. the weight is only a guide line. As I pointed out in your other thread some live rock is very porous and light. What you are after is that kind. Surface area is the important thing with live rock. 20%-50% of the volume of the tank filled with rock is more then adequate as bio filtration. I use a lot, 240lbs in a 75g, because I like the look and don't have many fish.
Seachem reef salt
B Ionic supplements.
For the sump/fuge I'd make it as simple as possible. Use a 20g tank, silicone in a piece of glass that fits the inside of the tank. Have it cut so it's about 9" tall. Silicone it in place so that your fuge is about 2/3 the length of the tank, or 20". This will still leave 10" for your skimmer and return pump. Just have the overflow fall into the fuge part of the tank. Over the fuge I'd recommend a Lights of America cheap Fluorex 42W flood light. They are very cheap and come in the perfect spectrum for growing algaes.
That is a great place to start for about the most trouble free tank.
So what is a fuge? A refugium is a place for "unwanted" algaes and macro algaes to grow. By allowing the perfect place for algae to grow under the tank, your display will be devoid of algae. The algaes in the fuge will use up the available nutrients so that it cannot thrive in the display. By "harvesting", thinning back and throwing away, clumps of the algae you permanently remove unwanted excess nutrients from the tank. It also becomes an area for critters to thrive in unharmed by fish. Copepods, decapods, and amphipods will thrive. These will overflow into the return pump and end up in the display tank. Your fish and corals will quickly eat them up. A tank like this will grow most any coral you could ever want. After about a year you won't really need to feed the tank as it will become it's own ecosystem.
This is a lot of equipment and commitment, I understand that. The thing to keep in mind is that you can have much simpler set ups but when problems arise they can be devastating. I prefer to build "trouble free" and less maintenance tanks. You have several routes you can take. I recommend searching you local area for a reef club, chances are there is one. You could get most of this equipment used for a lot less money.
If time and money are a factor those custom nano cubes are working great ffor many of my friends. They are somewhat limiting on what you can keep in them but will provide access to about 3/4 of what is available to the reef enthusiast.
Stay in touch.