I want to start fly fishing. I can't envision doing much besides trout fishing (for now anyway).

What is a decent entry level setup? I don't want to spend any more than necessary. I will likely fish mountain lakes, rivers, and small streams.

Personally, I'd look for a 8.5' or 9' 5 wt for a good all around starter rod.
If you plan to fish a lot of small brushy streams, consider going with a shorter rod in the 7.5-8' range.
Budget wise, you can be all over the place but $100 to $150.00 for a rod should get you set up. Look at something like the Redington Classic Trout series.

The rod and line will be more important then reel. Just about any reel will work for how you plan to fish. Consider it a line holder, as you'll likely never see the backing.

You'll want to start out with a weight forward (WF) floating line. Some of the complete rod, reel and line set-ups come with a line, but they tend to be less then great.
A Cortland 444 would be a good option.

Mad,
What's wrong with having too many wonder wands?
OK, I'll admit I had seven 6 wts....but I sold one this weekend.
Would that be considered thinning the herd?
SF

Sold it off.
Had to wipe off the dust off to see what brand it was.
My buddy is putting it to good use.

By the way....
I have a 9', 2 pc, 3 wt Loomis IMX with sock and tube available if someone needs a light stick.
SF

9' 5 wt is the most popular fly rod sold in the U.S., and for good reason. It's close to perfect as an all around trout and pan fish rod. The Redington Classic Trout that Stonefish mentioned is thought by many to be the best of the lower price point offerings in the market. I think they are currently priced around $130. Other good value options are offered by Cabela's in their Three Forks (cheapest at around $65), RLS, and LSi lines. Any of those series can be offered on sale, so check often. I bought a couple Cabela's Three Forks rods just to see how bad a cheap fly rod can be, and they are incredibly good for the price.

Good fly lines are pretty expensive. My favorite is the Cortland 444 peach color that has been around for over 40 years. They currently run about $60. However, there is a rumor that the house brand sold by Hook & Hackle is a re-labeled issue of that well known famous line in olive color at around $35 or so. I bought one in a 3 wt to pair with my Classic Trout, and it casts like the real deal, although I haven't used it enough to know if it's as long lasting as the real deal.

The best deal I've seen on entry level fly reels are the many old cheap reels on E-bay that can be had for around $30. They originally sold for less than $10, last forever, are no longer popular, and therefore for sale cheap. Buy one, clean it up, oil it, and fish it for as long as you like.

The above is the good quality, low price alternative, that most newbies reject due to lack of high zoot cool factor, and then they go buy some POS Okuma because it has a disc drag that no one really needs.

I remember those days when I still knew how many rods I had.

Sg,
Have you considered taking pictures of them for better inventory control?

Myass,
Down to five 6wts now, sold two this week.
Now, what to buy? LOL
SF

Pretty much what everyone else has said, but I will add that your cast is everything (more so than your equipment). A great rod will make a poor caster look OK. A great caster will make a poor rod look amazing. Like Golf, it's hard to unlearn bad technique, so go slowly and get the basics right so you don't have to rebuild anything later. 5 wt. 9' medium action, Cortland 444 WF. Yes, WF. I'd stay away from stiff, fast action rods while you are starting out. It's about line feedback when you are starting out and a medium rod flexes more to transmit said feeling. Also get yourself a metronome and some hula hoops. When practicing in the yard, tie or strap your wrist tight to your rod butt. Do not break your wrist!

Once you put the pieces together and start fishing...learn how to fish without a strike indicator.

$200.00 and a 3wt Loomis IMX emerges from my closet like a graphite hatch and fulfills your wishes.....
SF

9 footer, 2 pc
I just don't fish trout much anymore, so it needs to find a new home.
SF

S, watch out! This one is trained in the ways of the graphite

Most definately, don't buy new. Like probably everyone responding, myself included, has gear they haven't used in years(like the populace), and either here/craigslist /ebay, you can get a much better than low end new for even less, and get better gear/whole package. New Reddington(sage) good rods.
...line adds up, and if you find someone with a float and a intermediate/sinktip and spare spool, they're loss is your gain. This forced me to go thru the "drawer" and I found a drawerfull of flylines/many not numbered, so need to figure out wt/let it go.

My first rod was a cortland 6wt as I was told 6wt was a good "do everything" rod. I soon upgraded to a sage 6wtSageDS and better reel and felt the difference(86?). Shortly became trout bum and cruised the rockies and a friend gave me a sage 9ft 4wt.....Still my go to rod and haven't used the 6 but a few occasions.
If you intend to fly/pack a 4 pc rod is handy, and haven't flown in awhile with rod so not sure what current TSA say's about 4.5ft aluminum staff....i'd look for 4pc if you intend to travel. Bottom line....buy a 4/5wt as your first rod.....if you need more go 8-9wt. My 6 still collects dust, but not selling cuz 'I might need it someday....Ha, Tom

Marry a 5wt so you can appreciate your 3wt mistress.