Well respected custom in-ear monitor brands include Westone, JH Audio and Ultimate Ears. There are a good few others as well. I would start by looking at which models these manufacturers offer that are in your price range and then use the search function to find reviews of them on Head-Fi. You'll probably find quite a lot of information via Google too.
If you're at the initial stages of considering what you want to buy, I think the best thing you can do is do as much research as possible into the different models and brands.
Obviously your personal sound signature preference will be a big factor in any choice and hopefully reviews and people's comments will help you get an idea of which manufacturer and model will suit your taste best.
