माघे सन्ति त्रयो गुणाः

उपमा कालिदासस्य भारवेरर्थगौरवम्।
दण्डिनः पदलालित्यं माघे सन्ति त्रयो गुणाः॥
upamā kālidāsasya bhāraverarthagauravam |
daṇḍinaḥ padalālityaṁ māghe santi trayo guṇāḥ ||

“Simile is Kalidas’ forte, Bharavi – density of meaning;
Dandi – simplicity and Magha possesses all three qualitites!”

http://www.gaudiyadiscussions.com/index.php?showtopic=1708 gives some outstanding examples of some of these poets and the above verse too (though there is some confusion between दण्डी and नैषध)!

उपमा कालिदासस्य

जम्बू फलानि पक्वानि पतन्ति विमले जले।
कपिकम्पितशाखाभ्यः गुलुगुगुलुगुग्गुलु॥

jambū phalāni pakvāni patanti vimale jale|
kapikampitaśākhābhyaḥ guluguguluguggulu||

This is an interesting one. It is believed that महाकवि कालिदास was once challenged by भोजराज to fabricate a poem that would rhyme with गुलुगुगुलुगुग्गुलु! To which कालिदास promptly composed the beautiful verse above, which refers to the falling of ripe jamun fruits into clear water, from branches shaken by monkeys, causing the sound of गुलुगुगुलुगुग्गुलु (splashing).

No wonder (though this by no means is any ample proof of the genius of the महाकवि), it was once said that:
पुरा कवीनां गणना प्रसङ्गे कनिष्ठिकाधितिष्ठित कालिदासः।
अद्यापि तत्तुल्य कवेराभावात् अनामिका सार्थवती बभूव॥
purā kavīnāṁ gaṇanā prasaṅge kaniṣṭhikadhitiṣṭhita kālidāsaḥ|
adyāpi tattulya kaverābhāvāat anāmikā sārthavatī babhūva||

"Long ago, when the best poets were being counted, they started with कालिदास, on the little finger. Even today, due to the lack of equal poets to his stature, the ring finger remains अनामिका, or 'unnamed'! 'उपमा कालिदासस्य'(simile belongs to Kalidasa)!"