My partner is male, but he isn't into toys for himself; I'd get him non-sexual gifts or outfits he thinks are hot (stuff that I wear for him). When we can either meet more frequently or live together, I'm hoping I get enough spankings to make a glove or something worthwhile, to keep him from getting more sting out of it than me.
What does your partner like? If you're thinking of clitoral vibes like the Bcurious, I think the MiMi or the Seed sound like the best investments, with the Siri and maybe the We-Vibe touch running up. Those are personal preferences, though.
I personally like the idea of some kegel balls, but they aren't really for getting off. I've seen some that are supposed to feel pretty nice when you're doing everyday activities, though (the larger diameter, connected balls are supposed to be easier, you don't have to focus on working out with them I think.) If she asked why her vagina needed exercise, I'd just mention that it's supposed to help make her orgasms stronger...
Something like a remote control vibe might be fun if she's into something you guys can use publicly. That's something more interactive, so you'd hopefully get some fun out of it as well.
If my guy was buying something toy-related for me, I think I'd appreciate a clitoral vibe or a remote control egg best (the egg appeals to my submissive nature, though, it's more suggestive of him taking control.) Dildos and vibes I think are more personal; different girls really do like different sizes and shapes, and I can't think of any insertable toys that would be completely universal. I'd say the We-Vibe II, but I've seen too many reviews of it not working for certain people's anatomies (and I think other toys could work for her on her own better, if she wanted that.)