I thought it would be interesting to keep a record of how the interest rate evolved over the last year at the most popular high-rate yielding online savings accounts (i.e. HSBC, ING, Emigrant). Since my memory is not so good, if you remember how much was the interest rate in a certain month, and when it changed, please post a reply.
Disregard whether the rate is for new deposits or existing money and consider whatever promotional rate is on for a given period.
Only online savings accounts that require no (or very low) minimums to earn this rate are considered.

Federal Fund Interest Rate is at the bottom. Here are the APYs:

UFB Direct - Premier Absolute Savings(over $10,000)
(formerly known as High Yield Money Market Savings, discontinued on 06/27/07)
06/27/07: 5.31%
12/06/06: 5.32%
09/13/06: 5.27%
09/01/06: 5.20%
08/15/06: 5.26%
06/30/06: 4.50%
04/04/06: 4.40%
03/10/06: 3.75%
02/28/06: 4.50%
02/17/06: 4.30%
01/02/06: 4.00%
09/27/05: 3.80%
08/23/05: 3.70%
08/19/05: 3.65%
07/20/05: 3.40%
04/05/05: 3.30%
???????: 3.20%

GMAC - Money Market Savings ($500+)
04/20/07: 5.30%
03/16/07: 5.10%
01/26/07: 5.00%
01/12/07: 5.10%
12/15/06: 5.20%
12/01/06: 5.25%
11/10/06: 5.30%
10/06/06: 5.25%
08/04/06: 5.00%
07/28/06: 5.10%
07/14/06: 5.05%
07/07/06: 4.90%
06/09/06: 4.80%
04/21/06: 4.75%
04/07/06: 4.70%
03/10/06: 4.65%
02/27/06: 4.60%
12/10/05: 4.30%
12/03/05: 4.10%
11/19/05: 4.05%
11/05/05: 4.00%
08/15/05: 3.45%
07/30/05: 3.25%
05/10/05: 3.10%
04/20/05: 3.05%
02/10/05: 2.50%

Presidential - Premier Savings (for balances up to $35,000):
10/23/06: 5.25%
06/30/06: 5.12%
05/15/06: 4.87%
05/01/06: 4.75%
04/03/06: 4.62%
01/31/06: 4.37%
09/26/05: 4.12%
08/16/05: 3.87%
07/05/05: 3.75%
05/13/05: 3.50%

Emigrant Direct - AmericanDream Savings Account:
09/30/06: 5.05%
07/28/06: 5.15%
07/04/06: 5.00%
06/22/06: 4.80%
05/26/06: 4.65%
03/15/06: 4.50%
01/26/06: 4.25%
09/20/05: 4.00%
07/22/05: 3.50%
03/14/05: 3.25%
01/05/05: 3.00%

HSBC Direct - Online Savings:
05/01/07: 5.05%
01/29/07: 6.00% (new funds only)
06/30/06: 5.05% (old funds)
06/20/06: 4.80%
05/18/06: 4.65%
05/01/06: 4.50%
01/30/06 - 04/30/06: 4.80%
12/15/05: 4.25%
11/04/05: 4.00%
09/01/05: 3.75%
08/11/05: 3.50%
07/07/05: 3.25%
03/25/05: 2.88%
???????: 2.75%

Capital One - High Yield Money Market (previous rates here)
01/17/07: 5.00%

Virtual Bank - eMoney Market
(has different rates for different balance tiers)
02/15/06: 4.60%
09/27/05: 3.55%
07/27/05: 3.40%
06/21/05: 3.25%
04/08/05: 3.05%
03/22/05: 2.80%
01/24/05: 2.60%
12/07/04: 2.30%
11/18/04: 2.21%
01/27/04: 2.15%

ING Direct:
11/29/06: 4.50%
9/05/06: 4.40%
6/30/06: 4.35%
5/31/06: 4.25%
4/30/06: 4.15%
4/16/06: 4.00%
01/19/06 - 04/15/06: 4.75%
12/31/05: 3.80%
Dec 2005: 3.71%
Nov 2005: 3.48%
Oct 2005: 3.40%
Sep 2005: 3.27%
Jul 2005: 3.05%
Jun 2005: 3.00%
May 2005: ?????
Apr 2005: 2.98%
Mar 2005: 2.53%
Feb 2005: 2.35%
Jan 2005: 2.35%

Intended Federal Funds Rate
06/29/06: 5.25%
05/10/06: 5.00%
03/28/06: 4.75%
01/31/06: 4.50%
12/13/05: 4.25%
11/01/05: 4.00%
09/20/05: 3.75%
08/09/05: 3.50%
06/30/05: 3.25%
05/03/05: 3.00%
03/22/05: 2.75%
02/02/05: 2.50%
12/14/04: 2.25%

I don't see we need to do this. The interest rate as a function of time is not so important. It is not like you want to predict that 3 months from now, it will go up. The higher the interest rate from ED or ING or HSBC, the better it is. End of story and no one even wants to remember when they posted on FWF that ING became 3% APR because now it is absolete.

HSBC went from 4.00% -> 4.25% after the December Fed hike IIRC.

I had the same curiosity about a month ago, and put together a graph charting rate changes since the inception of accounts (back to 2000 for ING) for no-minimums/no-fee accounts (the kind I'm interested in). Data may be slightly inaccurate, but should be mostly right, and is gleaned from a combination of old fatwallet threads, old threads on other forums, old press releases, and some digging at archive.org:

Historical online savings account rates

I updated the OP: only consider online savings accounts that require no (or very low) minimums.
Updated Emigrant Direct section.

Has anybody else noticed this: going to http://home.ingdirect.com (copy&paste to your browser) shows a different page than following the link from FWF: http://home.ingdirect.com. I guess they are showing a more appealing page to people refered by FW ?!

SweetCash said:I updated the OP: only consider online savings accounts that require no (or very low) minimums.
Updated Emigrant Direct section.

Has anybody else noticed this: going to http://home.ingdirect.com (copy&paste to your browser) shows a different page than following the link from FWF: http://home.ingdirect.com. I guess they are showing a more appealing page to people refered by FW ?!

I'm impressed, looks like ING has some pretty smart programmers, or perhaps FW gets a cut from every click. There's gotta be a reason why a link in FW appears as a redirect rather than a direct link, right?

I'm pretty sure it's done on the FW side. If you look at the source code of this page, for instance (in IE View->source) and you scroll down to see your post, you'll see that in the source code it has the ...redirect... code embedded in the URL to be clicked. I suppose any URL you put as a link in FW, they'll convert to a redirect. I don't know why they would do this, but perhaps they have a deal set up with certain companies, that if someone is redirected from FW, FW gets a cut from it. Like, some people have redirect links where they get a bonus if you use their link to sign up for an account etc.

Fat Wallet used to have a link to ING Direct in the forums but it was taken off.

I think ING Direct had interest rates as high as 6% at one point going back a few years.

Capital One has been lagging the pack lately, only 4.0% currently (but no minimum). I've got the historical rate changes in OP of my thread: Capital One Savings Account (4.00%) - now with better transfers.

It would be interesting to note which bank had the highest average over period of time such as 6 months or 1 year. This should of course be a weighted average for the duration. (ie $1000 invested at each bank would yield how much by the end of the time period.) This would be good info for those who don't want to move their money around often - though past peformance does not predict future results it would help to show which bank has lead in rates.