Finding a good Soundfont
Most soundfonts on the net are not very good, as they are made very quickly and without great accuracy. Some of the greatest soundfonts can be found at:
SF2Midi.com (Forum not recommended anymore; no longer maintained)
Free Soundfonts by Guray Dere
There are some other sites on the net, you only need to do a search for them.
Always remember that even if the soundfont is big in filesize doesn't mean it's good. Some of the smallest soundfonts can pack a musicial punch. Always test a soundfont before fully using it to make sure it's waht you want. To do that, download Viena and audition the soundfont using the virtual synthesizer keyboard included in the program.