They're coming, honest. I've been busy. Or something.
Firstly, this is a good calculator for testing your expressions - remember to set it on 'Replace' for the operation.
Anyway, some example RegEx strings for you. Firstly, remember the format is First Line Search String, Second line replacement string. Click on the display to get a better view of this s/shot.

Let's take a few and have a look.
4 Digit Extensions
This is quite a common one - a 4 digit extension that needs converting to a full E.164. You need to know your extension ranges (I.e. 8000-8099 for example, or 4100-4199 as another example).
So, let's look at the search criteria.
^(80\d{2})$
So, we're matching on 80** effectively, I.e. 80 and two other digits, that could be anything. So 8001 would match, 8101 would not.
The replacement string is +44163556$1. This will prefix +44163556 to our number giving +4416355680xx where xx are the last two digits that meet the search string detailed earlier.
Now, that's quite a simplistic one, and just works.
Let's look at a more complex one - what about numbers with spacing, say an international one like 001 292 292 2954?
Firstly, I'd like to make a point about the spaces. We've had numerous discussions with Microsoft with regards to whether you need to include the spaces in the search criteria. The initial understanding was that you do not. In fact, if you use the route helper tool (available in the Office Resource Kit) you'll see it never, ever, accounts for spaces in numbers.
From personal and corporate experience we've found this NOT to work when normalising from the AD through to the Address Book Service - you simply have to account for spaces within your RegEx expression.
To be clear - these two numbers are NOT the same:
001 292 292 2954
0012922922954
So, let's look at the search pattern for the above number scheme:
^00(\d)(\s)(\d{3})(\s)(\d{3})(\s)(\d+)
Looks quite complex?
^00(\d) )(\s) - this searches for a three digit number starting with 00. In normal wildcard terms this is searching for 00*. Ths \s is a whitespace character, so we're serching for a 3 digit string with a following space...So again in normal wildcard display '00* '.
(\d{3}))\s) - searches for any three digits with a trailing space - so '*** '
(\d{3})(\s) - same as above, searches for any three digits with a trailing space
(\d+) - any number of remaining digits
So, as you can see, the search string builds up. Use the calculator detailed above to test and evaulate them - it's not as hard as it looks!
Now, let's look at the replacement string.
+$1$3$5$7
Now, the 1, 3, 5 & 7 refer to the string classes as specified in the search string. Let's break down
(1)(2)(3)(4)(5)(6)(7)
001_292_292_2954
(1) = 1 (The RegEx expression removes the leading 00)
(2) = First space
(3) = 292
(4) = Second space
(5) = 292
(6) = Third space
(7) = 2954 (Remaining characters)
So, again, let's look at the replacement string.
+$1$3$5$7
A bit clearer now? You're building:
+12922922954
...and you now have the full E.164 number.
It takes a little perseverence with your first evaluation of the numbers however it's pretty easier when you have a good calculator to hand.
Good luck.