still pondering britrail pass..???

The site that you want is http://nationalrail.co.uk. Tickets for your dates of travel are available for purchase already, so go ahead and price your journeys with the actual dates you plan to travel.

Since you're going and coming back from each place, of course you'll want round-trip tickets (called "return" in British English). Even so, sometimes it's cheaper to get two one-way (or "single") tickets. The National Rail site will default to showing you whichever is cheaper.

There are two kinds of train tickets you need to know: The kind you need to buy in advance (called, conveniently, "Advance") and the kind you can walk up and buy at the station right before you go (which include both "Anytime" and "Off-Peak" tickets). With Advance tickets, you can save a lot of money, but you must travel on the specific train you booked. The difference between Anytime and Off-Peak is in the name: Anytime tickets are valid any time, and Off-Peak tickets can only be used after the morning rush hour is finished. Other than that, they can be used on any train on a particular route, so you can change your mind at the last minute about when you want to travel. But of course, you'll pay more for that convenience.

One way Advance tickets:
London to Canterbury from about £11
London to Portsmouth from about £5
London to Warwick from about £5
London to Stratford upon Avon from about £5

it's easy to save by just booking individual tickets - forgo the pass

Unfortunately, I don't think looking at average fares will be helpful in this situation. Great Britain has about the widest-ranging fares I've seen. What you will pay for a non-refundable/non-changeable ticket at the promotional price far in advance can be a small fraction of what you will pay if you buy the same ticket on the day of travel. To determine whether the Britrail pass is a smart purchase for you, you need to decide whether you would otherwise be ready to buy some or all of those tickets quite soon, or whether it's worth the extra money to you to maintain total flexibility and pay day-of prices.

The best source for fares is the National Rail website. For the maximum you will pay, check for tickets for the current date. It's probably too late to do that today, but you can take a look tomorrow morning. What you can do today is check the fares for the likeliest dates for your trips. I took a quick look at fares for around 8 AM on Friday, June 8.

Dates can matter a lot, as can time of day. Trains during commuting hours sometimes are quite a bit more expensive than those at off-hours, but these are fairly long day-trips, so I assume you will want to get an early start. As for the dates, Thursday and Saturday might be less expensive than Friday. It will be worthwhile for you to figure out what is likely to be the most expensive trip if you buy tickets late, and explore all the possible travel dates to choose the least costly one.

Finally, fares can vary by rail company/route, and those are linked to the departure rail station in London (of which there are many). If you have a preference for a particular station, that's something to consider while you're doing your research.

All fares are roundtrip and per person.

Warwick: £11 (Marylebone)
Portsmouth: £24.40 (Waterloo--looks cheaper--or Victoria)
Stratford-upon-Avon (use full name): £14 (Marylebone--looks cheaper--or Euston)
Canterbury: £34.10 (Victoria or Charing Cross, or the more expensive St. Pancras)

The Canterbury fare is an "Anytime" fare that--as I understand it--doesn't lock you to a specific train. I believe you can walk up and buy that type of ticket the day you want to travel; I hope someone else can confirm that.

As you can see, if you're willing to buy the first three tickets soon, you probably have nothing to gain from a BritRail pass.

The cheapest regional pass covering those particular routes is the BritRail London Plus Pass, per person:

• 3 Days within 1 Month $162
• 4 Days within 1 Month $198
• 8 Days within 1 Month $274

Senior discounts also available. Passes that cover all of England cost more.

Yes, there are a variety of fares available on each train. About $40 either one-way Off-Peak or Same-Day Return for each leg is a reasonable estimate. Passes also cover the Heathrow Express and other airport trains, about a $50 value roundtrip on different days. So the pass is about breaking even with those rates but Advance rates can be cheaper.

I'm guessing that you and your wife are 1st time visitors. If that's the case, here is my personal take on BritRail Passes for the UK. YMMV.

If you don't know what you're doing, are not accustomed to using a train, don't want to work out an exact schedule in advance, want to have as many things as possible wired down before you leave home, don't want to have to stand in a ticket line and figure things out with a disinterested ticket agent, or worry a lot about what can go wrong, you're a good candidate for a rail pass. :) . If you miss the train, get on the wrong train, get off at the wrong place, miss a connection, change your mind about your destination, or just want to leave later/earlier you just get on the next train.

If you're ok with figuring stuff out as you go along and want to travel as cheaply as possible, buy point to point tickets. Point to point for the sites you mention will be significantly cheaper that a rail pass.

Also of note is that as you go farther afield, the more expensive the pass can get. For instance, a pass good for the entire country is more expensive than one covering only the south of England.