In Mahayana Buddhism we can see various artistic expressions: Thangka and Songs of Milarepa in Tibetan Buddhism, Chinese and Japanese art also were influenced heavily by Buddhism. Is there any forms of art practiced by Theravada monks? Do you know of any monks who were painters or poets?
The arts—be it painting, sculpture, architecture, calligraphy, etc.—have certainly flourished in the Theravada communities of the Southern Buddhist countries (Sri Lanka, Myanmar, Thailand, Laos, and Cambodia). See, for example, this section of the Wikipedia article on Buddhist art or this chapter of the book Enlightened Ways: The Many Streams of Buddhist Art in Thailand. And here is a gallery of pictures that might be of interest. With regard to poetry, be sure to check out the Theragata and the Therigata.
These are pictures I took at the Laotian temple (in the US) I've been attending. I'm told the monks make the decorative parts of the buildings and the statues. I thought this was very interesting so I looked it up and apparently these traditional artistic skills are passed down among the Theravada monks in Laos. more information
Is there any forms of art practiced by Theravada monks?
Yes, the art of taming ones own mind. What ever art aside of this will for the most cases not be conform to Vinaya, not to speak of Dhamma-practice, and is for the most not allowed, not to speak of teaching such, trade or make favors with such.
Monks may paint demons, corpse, things which increase samvega in their Uposatha Hall. Nice looking things, if receiving, need to be "destroyed" of their shine and color.
Most decorations, if not simple done by lay people without involving of Bhikkhus, are actually not really allowed by the Buddha.
There might be cases where monks "teach by pictures", being assisted by artists. They may get engaged in erecting Chetis (relict buildings, graves of the Buddhas relics and those of his monks) to increase faith.
What ever else, even if broad usual to give favors for a live or trade..., one does well not to regard it as proper and allowed. Also sightseen and attending galleries, parks, guiding for such... is not proper for monastics, even formulated as rule for nuns.
Additions and discussion on it can be found here: [Q&A] Buddha-images are allowed by the Buddha (at least by monks)?
(Note that this is not given for trade, exchange, stacks, entertainment and akusala deeds, but as a share of merits and to continue such for release)