I recently bought from www.royaltyfreemusic.com and was happy with the price (for a full disc anyway) and the quality of what I got.

Cinescore was created with me in mind...a videographer with little talent in the musical department. Acid and the others are great but I need something that will quickly create a score, for the time length that I need, that is tweakable for different moods during the video, and is a great piece of music. Cinescore does that better than I could with more flexibility than I have learned to use (need more experience with it). Looking forward to the new packs as with each new one comes thousands of possible scores for that theme.
Randy

problem with cinescore: there is almost no library available.
problem with Sonicfire: there are tons of libraries but they are pretty expensive (for free music , i mean).
problem with Acid or magix or any sample loop editor, is you need to find the loops (you can buy tons of them , but again it has a cost and they better fit a techno or R&B style than classical music or jazz) and assembling them to make a real music (not only a background fill) require real good musical skills.
My opinion is that Sonicfire is the best (good music , easy edition) if you can afford the 1000$ it cost to have the libraries.
I am not sure, but it seems that libraries at 22Khz are free, while the ones at 44Kz must be puchased.
for the new Strata series (with discretes instruments you can mute) they cost the hell (about 1000$) but i think with them you would be ok for any occasion.
you will need a lot of disk space to store them (between 10 to 20 gig).