Reaper is an excellent all rounder from tracking, editing and mixing audio (eg guitars, vocals, drums etc) to orchestrating, sequencingm editing midi with VST & VSTi capabilities. There are hundreds of free synths available, here are some of the better ones:

http://www.novakill.com/killerz.htm
http://www.kvraudio.com/
http://www.yohng.com/rhode.html
http://www.espace-cubase.org/anglais/page.php?page=freevsti

You can use these with Reaper which pretty much gives you a free home studio packed with hundreds of top quality plug-ins. Enjoy!

BTW If you want to pay for very high end VST's check out EastWest Samples and Toontrack from drums.