Tea Infusers & the Bodum YoYo
There are lots of ways to infuse loose leaf tea, and most of them aren't very good.
Dropping looseleaf tea in a pot is a reasonable way to steep the tea, but then you can't stop the steeping without pouring all the tea through a tea sieve or something like it. For many varieties of tea, that will get you a cup of tea loaded with bitter tannins.
Tea balls are typically very small, meaning that by the time you put a little bit of tea in there and get it wet, it swells to fill all available space, which makes it harder for the tea leaves and the water to commingle freely.
Pots designed for looseleaf tea are typically a little better, but they often have a small number of holes (reducing freedom of water movement), or very large holes (increased chance of tea sediment in the pot, particularly for very fine herbs like roiboos).
Infusing baskets designed to be used in a mug or pot are often an awkward size or shape, meaning it often fits well in a particular mug or pot, but not in a wide variety of pots.
Fortunately, there's the Bodum YoYo:
It's a shapely stainless steel infuser that fits pretty well in a wide variety of teapots and mugs, with a tapered tall-and-narrow design and a wide brim. It is spacious, holding more than enough tea with room for water as well. It's perforated with many small holes.
If you're steeping very fine herbs like roiboos, these holes are still large enough to involve some sediment, but they're good enough for most purposes.
They're not particularly cheap, but they're not going to break the bank at $25-$35. There's a set available that comes with a bodum glass. They're durable and not too hard to clean. As with most infusers, tea leaves sometimes cling to the textured inside surface, which is a little irritating to clean, but that's not specific to the YoYo. We have four of these, and they're in constant use. I really like these.
There's a mesh and plastic version, but I haven't tried it, and it's not nearly as pretty. It also seems to be out of stock in a lot of places as of this writing; I hope that doesn't mean they're ceasing to produce it.