Gmail allows you to retrieve the email from other email accounts via POP3 (just as many desktop email clients do). The nice thing about it is that it will also filter email from that account and mark suspected SPAM as such.

This feature is found in:
Gmail -> Settings -> Accounts and Import (tab) -> Check mail using POP3

I set mine up to delete mail from Hotmail's server upon retrieval to prevent email clog up. Also be sure to tag your Hotmail, so it doesn't get mixed in with the important stuff. You may still need to log into Hotmail occasionally to prevent them from shutting down your account. I've thought about setting up another Gmail account to replace my beloved Microsoft email acct. but...