The phrase "a lot of" is commonly used to describe a significant amount of something, but there are several synonyms that can be used to add variety to your writing. "Numerous" conveys a large quantity, while "ample" implies that there is plenty of something. "Plentiful" and "copious" suggest an abundance of something, while "abundant" describes something that is present in great quantity. "Myriad" is another useful synonym that refers to a countless or vast number of things. If you want to be more informal, you could use "loads" or "tons of" instead. Ultimately, using a variety of words to describe quantity can make your writing more interesting and engaging.