A coffee filter would work fine. People also use a tea ball for this. It is also called a tea infuser or tea crucible. It is a hollow metal capsule with small holes in it, or it is made of wire mesh. You unscrew the tea ball, fill it with tea, drop it in your cup, let it soak for a minute, and then pull it out by its small chain.

http://www.amazon.com/dp/B0006SYA34/ref=nosim/?tag=yahoo-kitchen-20&creative=380333&creativeASIN=B0006SYA34&linkCode=asn

http://www.mrslinskitchen.com/index.asp?PageAction=VIEWPROD&ProdID=17393

http://en.wikipedia.org/wiki/Tea_ball

You can purchase empty tea bags (just like the ones used at Starbucks) from a tea shop. You can also purchase small size 1 or 2 coffee filters and put the tea in, fold over the top and staple it shut. You may need to leave it in the hot water a little longer because the filter is so much thicker than a regular tea bag. . .

I use little metal strainers to put herbs in my green tea. Surprisingly enough catnip makes tea taste wonderful. Its almost minty. They usually sell the metal strainers, which are small enough to fit into a mug, with loose tea. Also panty hose works wonders.