Are you trying to create one yourself and simply find cheap online hosting for it or are you looking for other online servers to join? There is a whole section on the feed the beast forums devoted to server promotion for the different FTB modpacks here: http://forum.feed-the-beast.com/categories/server-promotion.81/
No one is going to give you a free server. It's like giving someone a free computer for doing absolutely nothing. You should do some research first. If you want to set up a Bukkit server, read this. If you need to port forward, go to portforward.com (skip the ads). Also, make sure you have a fast enough internet and an up to spec computer. You should at least have a 10 Mb/s upload and a 20 Mb/s download speed (Mb is megaBIT a second, not megabyte.) You should also have at least a computer with 2.0Ghz processor clock speed and a minimum of 2GB is recommended (really, you want about 4GB).
no one is going to give you a free server host if your friends are in your house when they play (probably not) you can make a lan server but if they are normal people start your own server on your computer and port forward it