Creme de Banana (also called Creme de Banane) is a banana flavored liqueur that is usually 35 to 50 proof. It is not a very often used ingredient compared to it's more popular "creme" ingredient such as Creme de Menthe and Creme de Cacao.
Most Creme de Banana that you find is extremely sweet, artificially flavored, and neon yellow in color. This includes the usualy bottom shelf brands such as DeKuyper, Hiram Walker, and Leroux. Bols, as usual, has a slightly better product that is also slight stronger. This proofs the somewhat reliable rule that the stronger a fruit flavored liqueur is the better it will taste. Marie Brizard also makes a Creme de Banana though I have not tried it. It is likely a quality product if I can project from other Marie Brizard liqueurs I've had.
I used to stock a bottle of Bols Creme de Banana but have found that I use it so rarely that it's not worth keeping around. But I'm not big on the sweet drinks, so that's just me.
You will sometimes find Creme de Banana in tropical drinks, usually as a modifier to a larger quantity of rum. Sometimes these drinks are bastardized versions of classic Tiki drinks that were never intended to be made with Creme de Banana (like a Mai Tai). But a lot of drinkers like a sweeter drink and the aroma Creme de Banana imparts to the drink can make you think you're at a hotel pool in Cancun (that's a good thing).
Creme de Banana is also layered sloe gin and green Creme de Menthe in a Traffic Light. And you can find this banana liqueur in cream-based drinks such as the Dutch Velvet and the Banshee which at one time competed with the White Russian in popularity.
I'd be interested to hear how you drink your Creme de Banana.