For no particular reason, I am listing my top 10 favorite SAP transactions, as they relate to building and administering to SAP Workflows.
1) SWo1 - the Business Object Repository (nothing to do with BOBJ, sorry guys, we were here first). This transaction is perhaps the first place to look when you get some workflow requirements. Look for an existing business object that you can use as-is, or copy and delegate to your own. You can also (and should!) test your custom attributes and methods from here. Pronounced SW-OH-1
2) SWU_OBUF - Refresh the org buffers. A lot of workflow and task related info is buffered, so many times when you make a change, you will get frustrated that you don't see it right away. SWU_OBUF does the trick. For additional fun, I like to press the 'go' button three times and then make a wish. Pronounced SWooooh-OH-BUF
3) PFOM - If you are using the HR Org structure (or your own mini-HR org structure) to determine the correct agents of tasks, you will probably need to have a look here now and then. That is, assuming you work very nicely with your HR organization to get access. You can also display important stuff like Communication Records (infotype 1208) and relationships. Pronounced Pee-FOM
4) SWI2_FREQ - Find out which workflows are running in your system. You can filter by workflow template, dialog task, background task, or even enter a specific task. Prounounced SWEE-2-FREAK
5) SWEL - the Event log. Although you should not leave this turned on in Production, on occasion, you will want it on - say, when you move a new application up. Leave it on for a day or two to ensure that the workflows are triggering with the events they correspond to. Pronounced SWELL
6) SWETYPV - Event linkage. This transaction will show you which workflows (receivers) are linked to which events. A must-see if you are implementing a new workflow - as it should be linked to the event here (if you are a firm believer in the Publish-Subscribe paradigm, as I am, as opposed to triggering your workflows programmatically). Pronunciation on this varies from SWE-TIPE-VEE (my preference) to SWEATY-PEE-VEE
7) SWUD - Workflow diagnostics. One-stop shopping for a lot of workflow - until you need to dig deeper. Verify your customizing, see if there are inconsistencies in your tasks or templates and launch the test environment. Not to be confused with SCUD, which is/was a missile. Pronounced SWUD
8) SWDD - workflow builder. This is the place where you pull it all together, your decision tasks, methods, messages, etc. Do not let your manager see this, as then they will think that all you do all day is drag pretty boxes around on the screen. Pronounced S-W-D-D (sorry, there is just not much you can do with that). OTOH, if you need a mnemonic to remember the transaction, try SAP Workflow Design and Deploy?
9) SWI5 - answers that ever popular question "What is this thing in my inbox, and what should I do about it?" You can see what workitems are pending in a user's inbox, or workitems they have already completed.
10) SWI2_DIAG - Shows all workflows that are in error. Hopefully this will not happen often. But realisitically, it *will* happen. So use this transaction and get familiar with it. This would be an alternative from SWI1 (which you need the workitem ID for). Pronounced SWEE-2-DIAG
That's my top 10 list. I left out ST22 because I thought that was just too obvious.
What else? What would be on your top ten list (don't forget the pronunciation or the mnemonic device, if you have one and it's not offensive. There are few that I have that I should not mention online. :)