Seems like $ would be inviting confusion, since it's followed by numbers that can look kind-of like a dollar amount:
19vcWM6EEbQHVdN2W8NXv9ySgsPjbZ6gU3$64.20.45.38

means send $64.20 to my bitcoin address ?

Hyphen or underscore would be less confusing, but I think period would work really nicely:

19vcWM6EEbQHVdN2W8NXv9ySgsPjbZ6gU3.64.20.45.38
19vcWM6EEbQHVdN2W8NXv9ySgsPjbZ6gU3.skypaint.com

The advantage of that last one is it is a valid URL;  if a user pasted that into Firefox's URL bar or searched for it in Google the website owner could display a helpful web page explaining how to pay.

To get back to the original question, paying to a bitcoin addresses displayed on an https: webpage secured with a valid certificate is better.

When the bitcoin client supports secure connections to IP addresses, then paying to an IP address displayed on an https: webpage secured with a valid certificate will be just as good (security-wise, anyway).

Bitcoin doesn't try to solve the "am I paying who I THINK I'm paying problem" -- we need HTTPS and signed certificates and DNSSEC for that (or something similar).  Bitcoins are a small but really important piece of the payment puzzle...

Ahh, right, I see; I hadn't thought through the mechanism of the pay-via-IP-address functionality.

That brings up another possible man-in-the-middle attack for HTTP connections:  if you see a Bitcoin address on a non-secure web page, you can't be sure that you're seeing the correct address (a man-in-the-middle might have replaced it with THEIR Bitcoin address).  And ditto for sending your Bitcoin address to somebody to request payment (e.g. send it via email or in your forum signature and it might get replaced before being displayed to people who want to send you money).

I don't see the security risk of being able to intercept or eavesdrop on a Bitcoin transfer.

All transactions are broadcast to all Bitcoin generating nodes, anyway, and the transactions are impossible to alter or forge (because they're digitally signed).

A man-in-the-middle could drop the transaction, but SSL doesn't fix that-- if they're relaying SSL traffic they could drop your SSL-encrypted transaction, too.

There are good non-security-related reasons for encrypting Bitcoin transaction traffic, though (makes it harder for governments/ISPs to do deep packet inspection to selectively drop Bitcoin traffic, for example).