Hey handiman! Check out PSU, Waterfront (SW Ankeny & Naito, don't ride weekend days due to Saturday Market), Lovejoy Fountain, Ira Keller as Ross mentioned, and Vera Katz (east side of the river). NE 52nd and Alberta has a great skatepark with fun trials features near it (i.e., a playground). PSU and the Waterfront are my favorites in summer though.
I ride more BMX now then I used to, but I'll be back in Portland near the end of March for some riding!