This is a GREAT WEBSITE. I believe that this is the best site on the web for searching for Chinese character etymology. This site gives very good etymological information about thousands of characters, and explains often the history of characters. In this site, you search for the etymology of single characters. It will give the etymology of the traditional character, and will talk about the difference (if there is any) between the simplified version(s) of the character, and the traditional version.
The site gives many oracle bone pictographs, seal script pictographs, and other ancient pictographs of the character that you searched. It will usually give dozens of examples of ancient forms of the character. Often one of the best ways to remember a character is to learn its etymology, and so this character will likely make learning and remembering Chinese characters easier.
Although this is mainly an English dictionary, you can actually use this site to search individual Chinese characters. For example if you search for 我，you get
en.wiktionary.org/wiki/我. This site often gives you etymological for individual characters. In addition, this tool often gives Japanese Kanji, Korean Hanja, and Vietnamese information of the character.
This site is another great source for Chinese Character etymological information. This site seems to have a slightly smaller database than yellowbridge.com or chineseetymology.org for etymological information of characters, but it is still a great source. Like chineseetymology.org, this site also will often show you pictographs of the Ancient and Archaic forms of the character.
Yellowbridge is one of the best online dictionaries that includes etymology information. After you paste in a Chinese character, you can click on the Character etymology tab to get etymology information about the character. Also, this site will show both for the Simplified and Traditional form of the character.
This site is one of the best Chinese -o-Chinese dictionaries and sources for Chinese etymology on the web. Assuming that you search for individual characters such as 馬, it includes Chinese etymological information, pictures of ancient scripts of the character, and shows variations of the character in different fonts. This will also give very basic translations into English, but this site is best used as a Chinese to Chinese dictionary. In addition, this site will convert the characters that you type into pinyin and bopomofo after you search. This site also allows you to search Chinese idioms.
This site gives good Information about the evolution of Chinese characters.
This site gives the etymology of roughly 100 common characters sorted alphabetically.
This link talks about why one would would benefit from studying Chinese etymology.