For "is":
* Verbs:
* Exists: "The problem exists." (Formal)
* Becomes: "The sky becomes dark at night."
* Represents: "This symbol represents hope."
* Means: "This means you can't go."
* Adjectives:
* Present: "The cat present in the room is mine."
* Available: "The service available to you is excellent."
* Phrases:
* There is/are: "There is a dog in the yard."
* It is/are: "It is hot today."
* It seems/appears: "It seems unlikely."
* Has/have: "She has a beautiful voice."
* Can be: "The solution can be difficult."
For "are":
* Verbs:
* Become: "They become friends."
* Remain: "They remain close."
* Phrases:
* There are: "There are many ways to do this."
* There is/are: "There are some mistakes in the report."
* It is/are: "It is the best time of the year."
* Have/has: "They have big plans."
Specific replacements for "is" and "are" to consider:
* For emphasis:
* "Is indeed" "The movie is indeed a masterpiece."
* "Are truly" "These are truly beautiful flowers."
* For formality:
* "Be" "Let it be known..."
* For a specific sense:
* "Seem" "The problems seem bigger than they are."
* "Appear" "The clouds appear to be forming."
Remember: The best replacement will depend on the context of your sentence and the tone you wish to convey.