Question: I have multiple site collections.

```
/
/sites/corporate
/sites/test
/sites/projects

```

I am looking for a way to navigate to the other site collections from each other and the root site collection.

How can I go about doing this?

Answer: 
You may define `New Heading` (Site Settings -> Look and Feel -> Quick Launch) with the required URL for other site collections URLs to be added to the quick launch menu.
if i get you right you want the same menu displayed on all site collections.... just like a website?

if so goto your root site collection homepage, site actions site settings -> click on navigation under look and feel -> make sure global navigation "show subsites" is checked. 

Make sure it looks correct under navigation editiing and sorting. Once that is done select ok and go back to homepage. For each sub site collection under navigation you need to do the same this time under navigation you need to select "display the same navigation as the parent" under glabal navigation.

If you were to create a new site make sure you inherit the parents navigation (select yes) under navigation inheritance.

You should now see the same top bar navigation throughout all from root site to any subsite