Total Recommendations: 3
You could call Princess Princess the brother anime to Maria Holic. The two anime involve crossdressing, are set in same-sex schools as well as having shounen ai and shoujo ai hints. Although both anime may have these hints there is actually nothing concrete from these genres, at most, a kiss.
Filled to the brim with stupidity, over the top antics and plenty of randomness; School Rumble and Baka to Test has much to offer, especially in the comedy department.
They are perhaps two of the longest shounen-ai's out there as well as being downright hilarious and simply entertaining. Gravitation is more fast-paced, to match its setting in the celebrity lifestyle and music industry. It's for people who like silly gags, zany characters and dark back stories. Komatta Toki ni wa Hoshi ni Kike is a lot more slow paced and is easy to appreciate with its slice of life approach. People who like sweet romances will easily fall in love with this. The main love interests in both shounen ai's share a similar trait: they don't have a great start, often at each other's throats but then changes (quite rapidly for Gravitation, and very slowly for Komatta) into mutual understanding and perhaps love.