Feedmyinbox: Enter a URL, an email address, and voila. Simplicity to its best. You can create an account and manage your incoming feeds too. Feedmyinbox’ inconvenience is the lagging time between the time a post is published and the time it lands in your inbox: Sometimes it may take up to 24-48 hours. Usually, the discussion around a post is already dead by then.
Notify.me: Notify.me can be used in a number of ways, but it is my preferred tool to be notified of new posts on sites I find important to follow. In notify.me dashboard, specify all the sources you wish to receive in your inbox, and it will send it to you. Notify.me is way faster than Feedmyinbox, but it will only send you the first paragraph of a post. I personally don’t mind it, but maybe you will.
Feedburner: Feedburner lets you burn any feed you wish. Therefore, just burn the feed you wish to receive in your inbox, and use the email update feature to have this feed sent to your inbox. The process is much longer than Feedmyinbox, but if you are into a little RSS-to-email hacking plan, then Feedburner’s robust RSS technology could be a good friend.
Yahoo Pipes: Again, a little like Feedburner, setting up Yahoo pipes to send you RSS updates to your inbox will take a little more time than Feedmyinbox. But just like Feedburner, if you are into a little feed tweaking, then Yahoo Pipes is definitely your best choice!
I think the best option out there used to be RSSFWD, but alas, it is no longer in service. I guess it was too good to be true. Know any other service? Please share in the comments.