[rocqua]

Most journals still publish a list of titles in the open, so you can 'follow' influential journals, and read the relevant articles on the arxiv.

[semi-extrinsic]

Google Scholar scrapes arXiv and coalesces the results with journal updates, i.e. it will show the entry for a new journal article with a clearly visible [PDF on arXiv] link when this is available. Google Scholar also scrapes institutional repos (at universities etc.).

[canhascodez]

Google Scholar is a service to humanity. However, I do wonder: how comprehensive is it?