I have issues with feeling sexy sometimes. I find the manicure/pedicure thing that Lorien suggested helps me a lot. I also find that getting into the right sort of clothing helps. It doesn't have to be lingerie (but it can. Sometimes just having a cute matching pair of panties/bra under normal clothes can make you feel more sexy). But even like, a nice dress, or a great pair of jeans. I will treat myself to a pair of jeans that are maybe more expensive than usual because of their fit if I'm especially feeling crappy.
Also, a hair cut. Sometimes giving yourself a hair cut (especially by a stylist you trust) can do wonders. It gives you a new outlook like 'okay, that was that girl, but now I'm this girl'.
Or even a facial.
Teddys are nice too, even if you can't have sex yet. I find that making my guy drool a little over me when I'm wearing a sleep outfit (even though I have no intention of having sex and he knows it) does wonders because I see *him* react.
Also, KY just came out with this new 'him and her' lubricant that is flavoured (strawberry for you, chocolate for him) and unlike other flavoured lube, it tastes good. It's meant for body exploration, so even if you can't have sex, you can put some chocolate lube on different parts of your body (elbow, neck, thigh, whatever) and have him lick it off you - it's sort of metaphorical for him saying you're tasty.
This last one is hard, and sometimes I have a hard time doing it, but sometimes when there's a part of my body I have issue with (like I have a few stretchmarks I think are super ugly and people would stare) I point it out to my boyfriend and tell him I hate them. Talking with him makes it better because usually he's like 'I never noticed that before.. you can barely see that. Why would you even look at that anyways when you have an amazing _____ to stare at'. It's a good pick-me-up.