If you're wanting to spend towards the top of your budget, then I'd recommend either the Asus ROG STRIX B250H Gaming. You can also go with the Gigabyte GA-B250-HD3, but the Asus has a little better of a sound chipset, and supports two M.2 drives. I also really like the Asus BIOS layout, right now - it's really doing it for me. Both are standard ATX-size boards, and will fill out your case nicely. They're both competing for near the same price point, but the Asus has a little bit more to offer.
If you're looking to go as low as possible, then the Gigabyte GA-B250M-DS3H would work just fine. It's a little smaller than the first two boards since it is micro-ATX, but it does feature 4 DIMMs for plenty of memory expansion. The only real drawback is that it only has 2 fan headers, so you'll need a couple Y splitters, or some Molex-to-3pin adapters.