Here are a few expressions that came in handy. I intend to add to this list as time goes on.
Regexp shown in Green, my comments in Red.

CSV Editing:

Remove spaces and tab characters at the beginning of a line:
Find what: ^[ \t]+
Replace With: don't enter anything in the field
Remove spaces and tab characters at the end of a line:
Find what: [ \t]+$
Replace With: don't enter anything in the field
Add “Hello” to the beginning of every line:
Find what: \(^.*\)
Replace With: Hello \1
Add “Hello ” to the beginning and ” World” to the end of every line:
Find what: \(^.*\)
Replace With: Hello \1 World (watch the spaces)
Find empty fields (i.e. “, ,”) with spaces or tabs in, and replace with empty field (“,,”):
Find what: ,[ \t*],
Replace With: ,, (just that, nothing else, just 2 commas)
Remove blank lines in a text file, by searching for two linebreaks next to each other, and replacing with one:
Find what: \n\n
Replace With: \n

Replacement Expressions:

Extract email addresses only from the following text: “Joe Blogs (job.blogs@blogsworld.com)”
This expression searches for 2 tagged expressions, firstly any printable characters including spaces up to the first open bracket symbol, secondly anything between the brackets. It then replaces the whole line with the second match.
Find what: ^\([[:graph:] ]+\)(\([[:graph:] ]+\))
Replace With: \2

Notes:

• The expressions above need the ‘Regular Expression’ condition to be ticked in the Find or Replace dialogue boxes for them to work.
• Text pad needs to be set to use UNIX not POSIX style expressions. To set this, open ‘Configure > Preferences’ (Ctrl+Q,P), find the ‘Editor’ settings, and untick the ‘Use POSIX regular expression syntax’ box.