You can add all sorts of fun little things to your webpage. The most interesting and informative are webcounters and guestbooks. Counters simply count the number of hits you have to your site. The more clever ones can tell you the referring page, so you can see where people come from - and therefore the most effective ways of site promotion and what people are looking for. Guestbooks provide a space for visitors to leave their mark on your site. They allow you, the webmaster/webmistress to see what kind of people are visiting your page.

Counters
There are a number of different kinds of counters you can use on your site. Some webspace providers offer one with your homepage, but it can often be more fun to find one for yourself. Some of the best I have come accross are these:
Sitemeter - has an option to have an animated counter, also a javascript version for more information about the hits to your site.
BoingDragon -  a really rather fantastic source for lovely graphical animated counters - pictures of dragons, faeries, flags...
The Ultimate Counter - has a 'random font' setting, so it changes for each visit to the site.
BeSeen - one of the most commonly seen hit counters, and one which a few of the homepage providers offer you. A variety of basic styles to choose from.

Guestbooks
I haven't had much experience of guestbooks, so I can only recommend the ones I have seen. Some webspace providers again will offer a free guestbook.
DreamBook - Dreambook offers a great guestbook. You can edit the entries, edit the forms of the guestbook, add your own categories and give your guestbook whatever look you want. However, you need to have some knowledge of html coding to properly customise the book. It doesn't have a quick preview page either.
GuestWorld - a famous and widely-used guestbook. You can delete entries and edit the colours.
GuestPage - You can pick up a layout from the ones provided, or customize one. Every entry made needs to be authorised by you before it is added to your page. 
BeSeen - This is the one I chose. Mainly because it was the only one I could get, apart from Dreambook and I have already described why I didn't like that one.

Another 'addition' to be considered is a webring (or webrings). For details on how these work, see the webring section on my getting started page.