Actually, depending on how complex you want to make your music, yeah, the reallygood ones cost money...sometimes lots of it =/ However, for simpler tunes, I'd say grab Finale Notepad. It's pretty decent. Basically for music composition in general, but it exports to midi file. As for a sequencer...um...*does some searching around real quick*
Well here's a classic...Anvil Studio sequences midis, and they have a free version. Has a Staff/Score view, but I think it's also got a piano roll. I tried it once a few years ago, and it was "okay" but they've probably improved since then.
One thing that's kinda handy for creating drum patterns in midi format:
MusicLab has a demo (time trial) of Drum Tools Performance Designer. It's quite handy for ppl like me who suck at writing their own percussion lines
http://www.frieve.com/english/musicstd/musicstd.html
Here's another one that seems to be free, and worth a look, but I haven't tried it myself. Think I might grab it actually, and give it a go.
And of course, Fruityloops has a demo version available, only problem is you can't save as project file, but you can export to midi/wav/mp3 formats still.
Of course, it'll take time to learn the software and get used to the layouts, and what you can do with them.
There's also some more stuffs on
http://www.synthzone.com/midiseq.htm
And I'd also hunt around electronic musician (Least I think that's the name of the site)
Also, if you have a soundcard that supports soundfont (SF2) files, you might want to take a look through
http://www.sf2midi.com for instrument samples. Be sure to read the reviews though. (the ones written by ppl who look like they know what they're talking about. Ignore the ones that say "ooh this is teh best1st th1ng 3V4R!")
As for some tips on getting started (being that I don't know how advanced you are with music writing) Grab Finale Notepad, it's a free download, and write up a melody with it, maybe add some chords or harmony, and some drums if need be. It also supports dynamic markings, which actually do work during playback, and they get exported along with the rest when you save as midi file.
Step 2: open the midi file in a sequencer and tweak it a bit, modify volumes, velocities, and tempos if need be. (At least that's what I use midi sequencers for. I generally -write- the music with notation software like Finale)
Step 3: (going that extra mile) You can grab something like fruityloops or some other sample based music software, and import the midi. Switch out the instrument patches with higher quality patches and experiment with different effects, tweaks, Equalizer settings, etc. (one of the reasons I adore Fruityloops, actually) And export to wav or mp3 when your satisfied with it. ALthough certain demo plugins/FX things probably won't export.
My preferred method for step 3 is using various high quality soundfonts. One place that's great to look for these is
http://www.sf2midi.com Also, I'd recommend grabbing whatever the last release of the Fluid Soundfont by Frank Wen. Although it's a whopping 150mb or so -.- But they work well in fruity with some tweaks.
Anyways, hopes this helps you all a bit. I'm no pro by any means, but I think I do fairly decent work considering I'm an amateur and hobbyist hehe. There's a really nice Fruityloops bible/faq/tutorial/guide forum on the remix forums over at Overclocked Remixes. If you do end up using Fruity, I highly recommend doing some reading over there.
My personal current Software: Finale Notepad (whatever the current version is)
Cakewalk Homestudio 9 (for midi sequencing)
and FL Studio 5 demo (AKA Fruityloops)
Damn this turned into a long post *cough* sorry bout that...I tend to get a bit chatty/helpful when it comes to writing music
