- love in idleness
- butterfly flower
- kiss me quick
- a kiss behind the garden gate
- three faces under one hood (also "two faces under a hood" and "little faces.")
- varigated violet
- bullweed
- love lies bleeding
- banwort, bonewort or banewort (Saxon names applied to a number of flowers, including the yellow pansy. The OED doesn't list this name as being a synonym for the Viola tricolor, though, so take this name with a grain of salt. )
- Pink of my John (also Pink-eyed John; the one is probably a corruption of the other)
- garden violet
- wild or field pansy (a common name in England)
- heart's ease (another common English name)
- stepmother (comes from German Steifmutterchen, "little stepmother" - I believe the Swedish and Danish names may be similarly translated.)
- Johnny Jumper (maybe a corruption of - or the source of - Johnny Jump-up)
- ladies' delight
- bird's eye
- call me to you
- gentleman tailor
- kiss and look up
- tittle my fancy
- (possibly) fairy buttons
My completely spurious theory about the pansy/pensee connection is that it's actually a Victorian creation, not an earlier one. While it's true that Ophelia refers to the pansy as the "flower of thought" it may be that she's obliquely referring to its other common names, those which associate the flower with meaningless physical affection or love affairs, such as love in idleness, love lies bleeding, or kiss me quick, and thus commenting on her doomed affair with Hamlet. Shakespeare was certainly conversant with "love in idleness," as that's the name he uses for the flower in Midsummer Night's Dream. The Viola tricolor, furthermore, was commonly used as an ingredient in early modern love potions; Ophelia may, therefore, be referencing the flower as the flower of "thought" ironically, since Shakespeare's take on love tends towards the physical and impulsive, rather than the distant and rational. Of course, another ironic use of the reference to a flower of thought is to consider it in relation to Ophelia's burgeoning madness, and Hamlet's sham(ish) madness. (And, of course, "thought" is one of the play's major themes - but that's not really something to get into here!) One could even argue that she's suggesting that Hamlet may have drugged her.
Anyway, my suspicion is that the Victorians (who were entirely gaga over the language of flowers) may have taken the line from Hamlet and poked at it a bit to make the pansy represent thought. It's certainly much more fun to consider that line from Hamlet as being ironic commentary on vain love and madness than to take it at face value.