Mmkay, I feel like I have many of them, so I'll share some notable ones below.
Pokémon - This one is fairly obvious, considering that this started the Pokémon craze everywhere, including in my country. It has run for pretty long, and I still remember the infamous original theme, either in English dub or Japanese original.
Power Rangers - Yep, I knew one since around Mighty Morphin Power Rangers days (and no, I'm not referring to the recent movie). However, I didn't knew Power Rangers has spawned many seasons because I didn't see the other series besides of MMPR when I was a kid, at least until when I'm a teenager. Besides of that, I also have some share of Super Sentai (the origin of Power Rangers itself) because the local TV wants to air them as well.
Cardcaptor Sakura - I can say this is one of my childhood as well, and the version that I watched is dubbed directly from Japanese source. I still remember Sakura's quest to catch the cards, and I still remember when I enjoyed the show a lot whenever I watched it in my local language or in Chinese language. However, at times I'm not sure if I could keep up with all those marathons in a certain Chinese cartoon TV channel.
Other notable mentions are three Eldoran anime series (which involves kids who control the mecha), Doraemon, Digimon, Blue's Clues, Dora the Explorer, Tom and Jerry, Ultraman Cosmos, Winnie the Pooh, Hoshi no Kirby (yep, they dubbed it from Japanese source), Sonic X, Road Runner... hoo boy, looks like I have too many list to count if it comes to my fave childhood series.