Flowers are such a personal choice that you need to figure out what
your gf likes. In general, girls are not homogenous (like orchids!) and for them, finding something they are secretly after and/or shows a lot of thought wins brownie points.
For instance, many orchid fanciers think cattleya hybrids are the greatest thing around - I find most of them too showy and frilly and lacy and don't really like them at all (my gf agrees).
I imagine you need to find the perfect balance between something that looks good and is fairly easy to care for. Nicely scented is a bonus too. In that regard, some of the
Zygopetalum hybrids are great.
I've often wondered why girls like cut flowers and other ephemeral gifts so much (dying plant sex organs are apparently very romantic...!) as opposed to something that will last; someone once said it's because it then gives you an excuse to go out and get more and show that you (still) care or something like that!
There are definitely red orchids out there; off the top of my head, there are red cattleyas (and hybrids), red(ish) Masdevallias, red phragmipediums (
bessae and its hybrids) and of course,
Disa uniflora, although I personally think they're impossible to keep.
Of course, if your gf really wants cut flowers, try and find something unusual in that regard; mine really likes tulips. I've always found roses hugely over-done, and I'm not sure about picking a plant that is covered in spines as a symbol of romance!
I'm sure some ladies will throw in their ideas too.