I really like Mortar's "humorous underdog" vibe and philosophy. It seems like they're a full service agency. It's a bit unclear who they are as a brand though; their website content can either be refreshingly funny or simply obnoxious. It seems they use a lot of neutral tones and desaturation to communicate their concept of simplicity.
Their identity design work for the San Francisco Aids Foundation is pretty strong:
http://mortaragency.com/what-weve-done/work/san-francisco-aids-foundation
