Formal:
* J'aime beaucoup. (This is the most common and literal translation.)
Informal:
* J'adore. (This means "I love" and is a stronger expression of liking.)
* J'aime vraiment beaucoup. (This adds emphasis to "like very much.")
* Je trouve ça super. (This means "I find it great.")
More specific options:
* J'aime beaucoup ... (something specific). (For example, "J'aime beaucoup le chocolat.")
* Je suis très fan de ... (something specific). (This means "I am a big fan of ...")
The best option will depend on the specific situation and your relationship with the person you are talking to.