Words such as Micro$oft and Kei$ha are examples of satiric misspelling:
A satiric misspelling is an intentional misspelling of a word, phrase or name for a rhetorical purpose. This is often done by replacing a letter with another letter (for example, k replacing c), or symbol (for example, $ replacing s, @ replacing a, or ¢ replacing c). Satiric misspelling is found particularly in informal writing on the Internet, but can also be found in some serious political writing that opposes the status quo.
The term also finds mention on Google Books.
3-peat is a contraction of three-peat1. From there, it's simply a question of replacing the three with the numeral (like we do with two-year-old/2-year-old). 3peat (sans hyphen) could perhaps be classified under one or more of leetspeak, SMS language, or as a grammargram or rebus.
I don't believe that Excite@Home really qualifies as it's effectively a portmanteau of the names of two companies, Excite and @Home. The latter is an ISP and its use of @ is self-evident.
1(the construction threepeat has apparently been registered as a trademark – threepeatedly