Your iMac will be fine with almost any router, no need to have an Apple router. The Apple one may be better depending on what you need, but almost certainly more expensive.
Wirelessly posted (Mozilla/5.0 (iPod; U; CPU iPhone OS 2_2_1 like Mac OS X; en-us) AppleWebKit/525.18.1 (KHTML, like Gecko) Version/3.1.1 Mobile/5H11a Safari/525.20)