What to buy next?

Next purchase should be an interface - you will be limited the most with your onboard sound card.  You can get some *decent* cans for about 50 bucks (and you will want to get monitors as soon as possible anyway and you'll need the interface once you do, but the $50 cans will be good for tracking then).  Mics you can get by with the dynamics for a good while (or pick up those Monoprice ones for cheap).
 
 
Note - different people have different definitions for *decent*.

Well, I've got to disagree with Cactus, cheap does not automatically equate with worthless. It is true that there are worthless products that are inexpensive, and it is also true that there are expensive products so esoteric, they are useless for everyday use.
 
Personally, I shoot for the the 'knee' of the value/quality curve. But for those on a budget, there are plenty of choices of good-sounding equipment. Before knocking someone, just remember the context in which that user finds themselves.

The saffire line is a good bet.  There have been a lot of people here who have had success w/ it, which is the best thing to go on.  Or the roland line.  The octa capture is getting blown out now, tho it is a bit more.  I bought a TC Konnekt 48 when they got blown out once - got it at half price and have never looked back.  But in general your bang to buck is very good in interfaces.  You may want an outboard preamp, but the interface preamps are pretty good, whle converters are cheap these days and do a great job.  combine those and you have a unit that should last a while and won't hold you back soundwise for the most part.
 
One thing is look at how you work.  If you do mostly in the box productions spend the first money you have on an interface.  If you do a lot of dubbing of acoustics you still need that interface, followed by an OK mic.  I mean, really, those will get you 95% of the way there once you learn to use them. 
 
If I was starting out today building a home studio and knowing what I do now I'd spend money on above average stuff.  The Forte or audient interface would give superb conversion and a good preamp or two ($500).  A good condensor mic for vocals ($200-300).  If I was recording electric guitar a cheap ribbon (-$100).  I bought an mxl just to fart around w/ and love it on electric guitar.  It also works nice doubling w/ my oktava lcd on female vocals.  They blend together well and that might be a way to get rid of some of the chinese shrillness of the cheaper ldcs - the oktava is much more a mid-forward design and the ribbon fills it out.  An interesting way to go might be a oktava mk102 sdc and a micheal joly k47 head.  You can do it cheaper but he sells it for $750 and you get a very good sdc and the ldc.
 
Once I had a stereo sdc and ldc then it is time to look at outboard preamps.  $400 for a warm audio or focusrite ISA one; $600 for a warm tone beast, which is one of the more flexible preamps around at any price (which sounds crazy for a mere transducer, but can add a bunch of different textures to your sound).  As you can see - high end recording starts costing money, but that last 5% of a professional sound costs real money.  About $1500 for an entry level, pro recording channel (mono) if you do the math.  If you spend that you can't blame the tools, so it is wise to know what you are doing before slapping down that much green.
 
But first find  an interface that works w/ your specific computer.  Most should, but it might happen that brand X doesn't like your computer configuration.  Try brand Y.  Hardware wise, they are all pretty much the same at the same price point.  If someone sez night and day between two $100 interfaces you figure they are lying to themselves.  There is only so much difference when you are working on such a tight budget.  Get the interface that ... well, interfaces w/ your computer the best.  Start making music, and learning.
 
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