In S04 E20, "The Herb Garden Germination", Howard starts his proposal at dinner at Leonard's place, but Bernadette cuts him off midway, saying yes.
Jake Peralta proposes to Amy Santiago in the most Jake Peralta way possible: undercover, during one of the precinct's Halloween heists.
In S08 E12, Barney reveals to Robin the final step of his playbook, "The Robin": "Hope she says yes." As Robin reads this, he kneels down & proposes.
Season 5 premiere sees Jim getting down on one knee, and proposing to Pam at a gas station on a rainy day.
In the Season 6 finale, "The One With the Proposal", Monica surprises Chandler with an old-fashioned, flowery, candlelit proposal.
In the iconic S05 E05, "Halloween Surprise", Ben surprises Leslie with a proposal and a heartfelt speech.
In the eighth and final season, fans were treated to not one, but two proposals from Stefan to Caroline, once in S08E02, and once in S08E12.