Since I don't rightly know if putting the actual music onto my blog will make Maestro yell at me, I'll just use the Youtube versions for now.
There's something about the simple, catchy tunes in a certain sort of anime BGM that appeals to me in a deep, primal way. They would probably not win any music awards, and bear more similarity to muzak than anything else, but it's the happy, bouncy sort of backgound noise that sticks in the mind as indelibly as the girl from Ipanema.
I suppose I noticed it first with Azumanga Daioh and "Saa, hajimari yo", which later acquired vocals in "Kaze no Iro March". It's the sort of BGM which fits a slice-of-life series, and I admit that I only use "slice-of-life" as a convenient well-recognized term to differentiate from, say, sports or action anime. What I mean by "slice-of-life" is the sort of story which does not focus on being the strongest or the classical Hero's Journey or some sort of dramatic revelation or other. Rather, it's the quiet, everyday, unremarkable happenings of the characters going through their daily routines. A group of friends, being friends.
This can obviously be present in an anime of another overall genre, since character interactions are an important part of almost every story, apart from the more Artsy (or grandfathered) sort. What I speak of are the moments where sweeping orchestral scores or ominous Latin-esque chanting would be out-of-place, as are delicately sorrowful strings or lonely soloists. Moments of simple happiness, the sort we can experience ourselves in our own lives. I'm a great believer that life should have its own soundtrack, and these tracks make it all worthwhile.
Admittedly, I usually have to have seen the source anime before the full impact of the BGM can be felt. This may be why I tend to mentally recite the spiel about the nonexistence of Santa Claus whenever my mp3 player turns up "Itsumo no Fuukei".