I can't really talk about the freeware stuff as I don't use any of it, but do a search on
http://www.kvraudio.com/ - they have a huge database of all the VST plugs and softsynths, free and commercial (IIRC you can filter for freeware only when you search). There's bound to be stuff out there. There are also a number of soundfonts lurking around, which can be loaded into any soundfont player.
Most recording software will have a built in step sequencer, a staff view, a MIDI Event editor and often even some kind of keyboard view - any of these can be used to enter notes in manually. You could also use something like the Virtual Piano from AnalogX - a software keyboard that can be played from your PC keyboard or even with your mouse, outputting MIDI notes.