Since your girlfriend bought you Clinque Happy it gives a general idea of what types of fragrances she would like. I'm willing to bet she likes light, clean, citrus and strays from the spicier heavy scents. Judging from that here's a list according to her taste I think she would enjoy.
Prada Infusion D'Homme - clean, fresh soap
Mugler Cologne - fresh green irish spring soap
Clean French Milled Soap - the only worthwhile fragrance of the Clean series, and this smells pretty good, despite it being marketed to women it's unisex
L'eau D'iossey - complex, citrusy, fresh, slightly floral and veyr long lasting
Chrome - musky floral with slight citrus
Light Blue Pour Femme - despite it being marketed towards women it has a masculine feel and many men wear it. clean fresh lemon laundry
Some I wouldn't recommend would be
Rive Gauche - more mature barbershop smell
Gendarme - clean but rather boring
Prada Amber - feminine smelling hotel soap
I tried keeping the fragrances relatively inexpensive since Clinque Happy is.