Aswell as Valentine's Day, other times of the year to get engaged are during the summer when the sun, sand and sssssssh! Sangria gets you all emotional - then there's Christmas when New Years is fast approaching and you decide to make an honest woman of her ......
They say you should spend at least a month's wages on 'The' ring I think it should be more personally but after all a ring is a ring and love is what matters. (cough)
But just in case you do earn in excess of 10k a month here's some inspiration from Harry Winston ......
http://www.harrywinston.com/

The brilliant cut
The classic pear

The Emerald cut

Oval cut

Marquise cut

The Emerald cut trilogy...
What ever you choose good luck! FYI - your always better buying a smaller stone than a fake stone! Just saying