Hayate no Gotoku!!

Both Toradora and Hayate no Gotoku (HnG) are similar because both of them are slice of life, romance, and also include school life. In my opinion, HnG is better than Toradora because it has more comedy and action. HnG is full of parodies, and sort of like a harem, and there's a lot of comedy. I recommend HnG for any age but it's not as romantic as Toradora (kisses on the cheek couple times, which is basically it). 

Over the top butlers and references galore. Both are similar in many aspects and enjpy parodying other animes/etc. 

both are harem and both have very strong male protagonist 

both have strong male character both main male character confuse other girls both have same felling and humor both have very rich girls and they try to lead a normal life both the male character parents have left the child alone and gone somewhere both the main male characters are understanding  

about a tsundere girl who fall in love with a boy which is her servent,and there is a harem in this anime 

Both are hilarious animes that have a lot of references to other pieces. Also find that the characters are quite similar: Hina and Minami are both Tsundere Hayate and Akihisa are both dense as lead Segawa and Aiko are both teasers Also both shows like to put their main protagonist into questionable outfits.  

this is very similar to shakugan no shana because nagi and shana are almost exactly alike. and hayate and yuji are almost alike. :D 

Somehow, Hayate, and Kamjio Touma seem to have more in common. They both seem to get themselves into difficult, and usually awkward situations. The end result is either laughs, or some action scene, which are both present in both animes. This can recommendation can also be towards the first season, as well. For a more simple similarity, they're both produced by JC Staff (Not the first season). 

Both feature a cast of characters ranging from strange to deranged. Especially the student council president has striking similarities (from popularity to power). Kujibiki Unbalance as a part of the Genshiken Universe is a little more serious than Hayate no Gotoku and somewhat retro, but nevertheless entertaining. 

Similar seiyuu, similar art, similar characters, similar genre (style of humor), similar relationship between characters. :P This one totally reminded me of the other! xD 

Both share the same kind of comedic atmosphere plus they both share half the same seiyuu cast. 

Both are second seasons of a great parody anime. They are both alike in their comedy and atmosphere. Plus, both have Kugimiya Rie in the main voice acting cast. 

Both anime is about a rich kid with their maids and butler except "He is My Master" only have maids. It's really similiar but a little more ecchi. 

Comedy! Comedy! Comedy! Both are romantic comedy, atleast to me. Both have relatively the same portion of comedy vs romance (although it does depend on the situation), however while seto no hanayome have more of the "over the top" kind of comedy, HnG focuses more on gags and little jokes.