I make myself weigh myself, I hate the scales but love the feeling of satisfaction when it tells me I've lost some. Also as said, look at pics of cosplays you want to do. At the moment I'm not going for anything small or skimpy. I keep thinking of how I need to work on my legs for Celes (FF6 Yellow Outfit) or my stomach for Tifa (FF7 advent children).
Even for my main cosplay that I'm going to start on soon (Georg Prime- Suikoden V). It's fully covered and rather baggy so nothing's being shown so I think to myself "Come on! He's a knight! He's going to be in good shape".
Also, I agree with music, part of my workout is (and I hate to admit this) the cheesy just dance games on the wii. I set it to shuffle and play music I like through youtube and make a fool of myself "dancing" around. Seems to be working at the moment